PCPartPicker. It does everything for you and gets you nice deals on the parts. You can also screencap builds you come up with and ask people on Holla Forums or /tech/ for advice. As for actually building the thing just look up tutorials on Youtube.
Intel i5. Don't bother with i7 unless you're doing advanced video production, you won't see a difference but your wallet will. Also don't bother with overclocking, so don't bother with their k series processors. It's a lot more money for a slight benefit, and you should be fine without overclocking.
If you want to go for AMD for some reason the 6350 and 8350 work. I haven't run into many problems with my 6350 but I don't play many newer games. Or you could wait for their Zen processors, which are supposed to be better.
Nvidia: Go for the 980Ti if you want something fancy. If you're on a budget the 780Ti should still work fine, but Nvidia won't like that.
AMD: Wait for the RX 480. Anything from the R9 270X onward should be good enough, but newer games are more demanding.
They're usually specific to the processor. Just get something that works and doesn't have any glaring flaws. An Intel motherboard is different from an AMD one, so double check.
If you want a little PC get a little motherboard.
Tower PC = ATX
Smaller PC = MicroATX
Tiny PC = MiniATX, sometimes called ITX
Doesn't matter much for towers, or you could make your own. I have a Corsair 300R and it works nicely. No frills, lots of space, grill on the top for convection.
If you want a little computer get an ITX motherboard and Fractal Design Node 202. It's a bit harder to build in, so I wouldn't recommend it at first
Add up the power requirements for all your stuff, add a bit more, get a PSU that supplies that wattage.
Efficiency is important, as is build quality. You can skimp on a fan or case, but if you cheap out on your PSU you can fuck up your whole system.
I use a Corsair one but apparently they're not that good.
16 is overkill, 8 should be good enough. It's cheap anyway, so don't worry about getting more later.
A few fans should come with the case. As for the processor fan the stock one that comes with it is OK, but if you want to overclock or you don't like it running hot get a better one. The Cooler Master Hyper 212 EVO is good but make sure it fits in your case first. If you're in a colder country you should be just fine with stock.