well, depending on the controllers... most sequencers support what you plan to do with it. sometimes it requires 3rd party drivers though.

in regards to the octave range. i'll tell you i borrowed a 31key from a friend for a while and it was a mistake...

buy a 61key at minimal, 5 octaves is enough to do just about everything. there are a lot of other threads on midi controllers too so be sure to read up

I believe in cubaseSX which i use you can assign most mixer functions to outboard midi controllers. By default most software already recognizes things like mod wheel and pitch bend wheel and they are assigned as such. If you change those assignments for certain other applications you should be careful and save a template specifically for that. Otherwise when you are producing your mod wheel won't control your soft synths properly anymore etc etc.

Most midi keyboards these days have an octave -/+ control on the keyboard so you can play midi notes at higher or lower octaves while on a limited size keyboard. It's not ideal when playing piano parts that require bass and an high notes simultaneously, especially in a live situation. As was suggested i wouldn't go with anything less than 61 keys personally.

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Happy music making!