That's correct: Increase Maximum is what I'm referring to. You're also right about having to have a different type of ModMax/Increase Maximum for each type of outfit. You can, however, keep a person from having more than one genre of outfit with bits. Say 200 and 201 are two types of shields that are mutually exclusive. Set the availability of 200 to !o201 and vice-versa.
However, if you wanted to allow mixing and matching, you should use the token system mentioned a few posts back. That way, you can have, say, outfit 205 be required to buy outfits 200 and 201, and have each delete 205 when bought and grant 205 when sold. That way, you can mix and match, but cannot exceed the maximum number of tokens (outfit 205) that each ship comes with.
There's a nice list of what outfits the AI can and cannot use here, hear the bottom. It's one of Guy's post.