... probably about the same as with any FPS system.
Have you checked out the TornadoTwins' FPS system on the asset store? I believe it's a free package.
As for the rest, well, that's going to be difficult because elements of game play are going to be different based on what specifics you're looking for.
Things like how you're going to handle weapons, if your character can level up with experience, in-game currency or ammo management. stuff like that.
But if all you want is a basic FPS control system and would rather focus on the art and other visual assets, maybe check out the asset store. there are a lot of free packages there (and some paid) that should get you going in the right direction.
