This is not a quantifiable measurement. This term mainly describes the product line of a CPU. As in:
i3 is the budget line.
i5 is the mid-range line.
i7 is the high-end line.
i9 is the enthusiast line.
You can somewhat reliably expect products from the same generation to have their performance tiered accordingly to the schema above. The price to performance ratio is inversely proportional to this - higher lines tend to offer greater performance at an even greater price.
However, the higher number does not always directly translate to better value performance. High-end CPUs from a couple generations ago tend to lose in performance to mid-range CPUs from the current generation. Therefore, when building a new PC, attention needs to be paid to ensure that the CPU is sufficiently recent - while older models tend to drop in price as newer models are introduced to the market, at some point, you could've gotten a more recent CPU with better performance for the same price.
With that said, this only covers Intel's side. There's another big name in the CPU industry, AMD, who has been on the rise lately. Although having been in Intel's shadow for the longest time, they are now also producing viable CPUs for just about any range of customers from budget to enthusiast. I'm throwing this in here as this choice directly affects the compatibility of other components, primarily the motherboard, as CPUs from one manufacturer are not compatible with the sockets of the other.
I suggest taking some time to think about which games you'd like to play on this PC now, and potentially any upcoming games you'd like to play in the future, and to check their minimum system requirements, as this will likely be the most intensive task your CPU will need to be able to handle. These will often be provided in the form of CPUs used as an example of what was used on a machine that runs the game well. You could then compare benchmarks of this provided CPU model on sites such as
UserBenchmark to find out CPUs which have similar performance as the example - maybe you'll find something that offers a better price to performance ratio.
Quad-core or is dual-core sufficient?
This choice largely depends on how much you're planning to run at the same time on your device. Luckily, it's a lot more technical than the iSomething stuff, so this is something we can quantify!
A CPU's core count roughly translates to how much it'll be able to process... that is,
at the same time. By default, programs will run on a single thread, which in turn runs on a single core of your CPU. It is sometimes possible, but not required, for developers to develop their application in a way that uses multiple threads across multiple cores to take advantage of end users' CPUs that have more than one core. The caveat here is that additional cores will
only benefit any program if it was written in a way that takes advantage of it.
So, a CPU with two cores will run a single-threaded game
roughly the same as a CPU with four or eight cores, provided that all other hardware specs are identical. A piece of software that can take advantage of as many cores as you have, however, will likely see massive performance increases the more cores you have - a common example of this is video rendering.
I'd call dual core the absolute minimum. A quad core CPU can provide great benefits if you are either running a lot of performance-intensive applications at the same time, or a single application that can take advantage of multithreading. The workload you described sounds like it's somewhere in the middle of these two - a quad core, although not entirely required, would be able to handle the multitude of applications that might be running at the same time more easily, while also leaving room for more intensive workloads, should you ever end up using anything that would greatly benefit from it. Unless doing so would burn a hole in your pocket, I'd recommend going for a quad core.
Clock speed 2GHz minimum?
This is one of those metrics marketing desperately wants you to believe are the most important thing out there. Why? Because "FIRST CPU THAT CAN RUN AT 5 GHZ!" sounds better than "we slightly increased the frequency over the old generation's model because we got it to run stable but the underlying architecture is roughly the same". While frequency
does matter, it is merely one factor that determines a CPU's performance. (I'd definitely raise my eyebrows at any CPU marketed to me as "recent" with a 2GHz frequency, though - not because it automatically has bad performance, but rather simply because it's a figure most often seen in older models or mobile versions of the current generation)
You can think of the frequency as a "multiplier" of sorts - specifically, a multiplier for the CPU's IPC, or instructions per cycle. This is what's used to measure a CPU's throughput - as in, how much it can process. The frequency then acts as a multiplier to this. Given
the same IPC, a CPU running at 5GHz has a 5 times higher throughput than a CPU running at 1GHz. IPC and frequency don't always increase at the same time, though - a CPU with a higher frequency may have a lower IPC than another CPU with a lower frequency, and the latter can still be able to outperform the former.
For example, an Intel i7 7700k running at a 4.2 GHz base clock is outperformed by an AMD Ryzen 7 3700x running at a mere 3.6 GHz base clock, due to the remaining architectural differences that make up the bulk of what determines performance. The former is three years older and yet tends to retail for 1.5 times the price of the latter.
The best way to tackle this issue is, once again, to compare benchmarks.
What memory cache size minimum to look for?
Ah, finally one I can answer with a general "the more, the better"!
However, it's also one of those things I'd call a lesser priority - not on paper (as it
does make a difference), but definitely when researching what to buy, as it is overall not indicative of a CPU's performance. A CPU with low performance but a bigger cache will very likely perform vastly worse than a CPU with high performance and a smaller cache. Fortunately, CPU caches tend to have more favorable statistics the better the overall performance of the CPU is, so I suggest looking for a good CPU based on its overall performance rather than based on its cache alone.
Ram - 8GB enough or need higher?
This one again depends very heavily on your most intensive workload (which likely is the games you'd want to play). The system requirements of said games will give you a general idea about this. A game that requires 8 GB RAM to run by itself, for example, will not run on a PC with 8 GB of RAM, as RAM is shared among all programs that run on it. Open up everything you'd like to have open at the same time (following your described workload above) and check your PC's memory usage.
For example, my PC with the absolute minimum that I need on a daily basis loaded sits at this memory usage:
You can see that 74 out of 128 GB are committed (reserved). This would be the
absolute minimum, as loading anything more will not fit in your RAM. (Not 74 GB, by heaven's sake! Replace that with your own result.
)
Once your RAM is full, one of two things happens:
If you have set up your PC to use a page file, a portion of your drives, such as your SSD or HDD, will be used like RAM. These are slower than your RAM, therefore dragging down your PC's performance.
If you do not have a page file, or your page file is
also full... well, anything could happen at that point. The program you're using may complain that you don't have enough RAM to complete the operation, or it might crash, or your entire PC might crash... yeah, you don't want this to happen.
You
don't want stuff to be
forced to end up in the page file, and you especially don't want to run out of both RAM and page file space, so the general rule here is to get
more RAM than you need, but
not too much more, as you'd be wasting money at that point.
Standard hard drive enough or need solid state drive?
While you don't
need a solid state drive, an SSD can
tremendously improve your PC's performance, as their performance is in general
vastly superior to that of HDDs of an equal price range.
With that said, I recommend... neither of the two options.
Why settle for one? Get
both! Put anything that requires performance on your blazing fast SSD, such as your operating system and installed software, while stuff that merely exists on your drive most of the time, taking up space but not requiring performance whatsoever, such as music, pictures, videos, etc. can land on your hard drive. This helps you to not eat up your SSD's likely already very limited capacity while also providing all the speed benefits having one brings you.
Graphics card... I have no idea what to look for at all
Better question:
Do you need one?
Chances are that whatever integrated GPU your CPU has (
if it has one - if it doesn't, yes, you definitely need a GPU) will be more than sufficient for your workload. If not, name an example game you'd like to run and I can point you towards the general range of products you should be considering to have a smooth experience both in regards to performance and staying close to the budget.
There are a couple more components such as the motherboard and the power supply that can't be overlooked... however, they depend on the other components, so I can't make any statements about these yet.