Pot size is a judgement call. Generally speaking, single coils get 250K parts, while humbuckers (or noiseless singles) get 500K parts. However, either will work with either.
The thing to keep in mind is the lower the pot value, the greater the load on the pickup, and the more high end response you lose due to impedance issues. Because of that, I always use 500K pots, regardless of the pickup design. If it's too edgy, back off the tone control a smidgen. The problem with the 250K parts is if the frequency response is diminished due to loading/impedance, there's no way to get it back.
As for capacitor values, again it's a judgement call. The larger it is, the more signal you lose as you move the cutoff point farther down the response curve. So, I generally use a .022μF part. It seems to give me a a fairly even response for the range guitars work in.