2004 Mini Cooper base. What does stage II require? Thanks for he help

 

Normally "Stage 2" is associated with the supercharged R53 or the tune on a turbocharged 2nd Gen.

 

Stages like Stage 2 are generally just marketing terms for packages of parts. So ignore that and build a plan for what your HP goals are. But with a non S it will be hard as they just don't make the power the S does.
Start with an intake and exhaust then go from there.