newbie question: stocking strings

[Charles Neuman]

I don't want to be one of those guys who doesn't fix broken strings. But
where do you start, in terms of stocking treble strings? Should I really
have every size (that's quite a big initial investment), or are there
common sizes I should start with?

Also, how bad is it to be about .003" off? That is, if I stocked sizes
that are .005" apart, then I'd be plus or minus .0025" at most. I'm
expecting some negative responses to that, but I like to hear them. I
assume levelling is an issue, not to mention tone and tension. But for a
cheap piano, does it matter really?

Charles Neuman
Long Island