+1 for this:
I'd suggest going for a 7,200rpm 3.5" drive
I have been using USB 2.0 external drives that are 7200 3.5" for years without issues for BOTH live recording and use in the studio. That being said, I don't do a lot of MIDI, it is mostly all Digital Audio so that may be an issue.
Also my track counts are sparse (typically between 16-30).
And my plug in count isn't all that high either. I try to get the mix right with minimal processing.
So bottom line take my experiences with a grain of salt & wisdom!