Might I add, the most you can max out a single stat by is 44 points. Then you'll need to pick a different one.
Not always 44, it depends on the stat.

Generally speaking, it's a relatively even split (or as even as it can be) for the types of materia you need. For instance, if a stat could go up by say, 33, then you would need 8 each of I/II/III/IV materia if you wanted to max it... plus a 9th of one of those types (not sure which one) because the extra has to go somewhere.

One notable exception is putting accuracy on a healer weapon... the innate small bit of accuracy that they put on healer gear past a certain level counts toward your melds already, so you'll only need a couple of tier I accuracy materia before you start needing tier IIs (of which you'll need a lot more if you want to keep progressing the stat).