OK, well I am not a pro, but I know there is a new supercharger for the MINI - higher volume. There were several posts over at Northamericanmotoring.com ( NAM ). Also Cosworth has a new head for the MINI that is supposed to be very good - I think it is sold thru M7 ??
If you want to do it all yourself - then all the normal mods apply - high strength rods, crank, bolts, pistons, etc..
Have a competent head man port and polish the heads - he / she should be able to set you up with a reliable high RPM valve train.
Check with your local race shops and maybe spend some time at the local tracks talking to the better drivers abd see who they use.
If all else fails check out the sponsors on MINI2 and NAM and e-mail them - see what they suggest.