arssanguinus, you are on the right track here. i once made a program where i could copy in recruits, 50 at a time, and it would apply my formulas, including modifications for potential. in this program, i would make sets of formulas, there could be multiple for each offense, defense, division, and position (although i only made 20 sets or so). now, i don't even use the program, but the exercise was invaluable. it REALLY makes you think about what makes a recruit good, and what stats are really only good when other stats are good, and what stats are multiplied by others, etc.
in my program, you could make arbitrarily complex formulas, often i'd use a bunch of if-then type statements too, for example, with work ethic, i felt the first 30 points were a hell of a lot more important than 70-100. i highly recommend you take the time to work your formulas, and continue refining over time, it is some great thought that will help you in all facets of the game, not just recruiting.
heres a couple tips on how you might want to approach it: one thing i did is, i made a few sets of formulas for different roles, not just for a position. for example, you can't apples to apples compare a pg who is not a shooter vs one who is a shooter, so i made a set of ratings for a non shooting pg, a shooting pg, a shooting specialist sg, a regular sg, a rebounding sg, and a rebounding sg who would play sf. it was very helpful to think about how all these roles were different, and how much perspective effects the quality of a player - that is, how he can be great in one role and just decent in another role, both of which may be appropriate for a player with his position.
another thing i did was, make each player's final rating a sum of a few common sub ratings. for example, a big man might be his offensive ability + defensive ability + rebounding + work ethic + misc other stuff, where each of those categories was a formula, in some cases, a very very complex one. the reason to do this is, it is MUCH easier to calibrate category by category. in calibrating your forumlas, you probably are going to look at some set of data, and look at one player then the next, and so on, trying to make sure the rating puts them in correct order of quality. well, that is hard to get a handle on - its much easier to say which big man is better offensively and how big of a difference that should be in their ratings (like should it be a 120 vs 150 or 120 vs 130?). also, this later will allow you to sort based on your needs - for example, if you just have 1 generic big man formula, and this season, you need 2, one really good offense, and one really good rebounder/defender, then you can get a lot more out of your ranking system, by looking not only at overall but the important, meaningful subcategories.
good luck in your pursuit! always keep in mind, you never want to just rely on the formulas, always eye ball it in the end :)
edit: i hadn't read everything, yes, you are right to break it into categories. but you definitely want to weight them. also, in a system where like, you have an offense and running the point category for a guard, you very easily can have a stat (like ball handling) appearing in multiple categories. that is a good thing.