That is irrelevant. If you get a proper i5 now, the only upgrade option you are sure to have is the i7-7700K, and if you are lucky there might be i7 of the next line.

Absolutely buy an intel processor if it is the right fit for you (=you are a gamer), but don't expect to re-use the mainboard for your next processor - only plan with that if you go with a Pentium G4560 for now. Then you can upgrade to a better processor of the current generation.

Essentially two options: Skylake and Kaby Lake (which is a slightly more efficient update of Skylake). And seems like no future beyond that.

Counting the individual SKUs is kinda pointless, they're just cut down versions of the same chip.