There is a big thread on this board called "Tamiya Mini Cooper" which will have all the answers you seek and more. Take a look.
Brief answer to your questions though (assuming your car really is box stock M-05)...
- You can't adjust the ride height on the kit shocks. Oil-filled dampers (CVA good, TRF better) and short springs are a brilliant upgrade.
- Actually, there really isn't anything you can adjust on the box stock kit. Just build it, run it and enjoy it.
- When you do buy those parts, get the aforementioned oil-filled dampers and springs, add a full set of bearings (so the car runs smoothly and quickly), and on an M-05 you should get a few parts to upgrade the steering system which is a bit wandery otherwise (hi-torque servo saver and aluminium steering posts are my suggestions).
- The final important bits of tuning (two of the most important really) are the tyres (run what the fast guys like at your track), and the diff (a diff with a stiffer action works better in the car). I run the M-05 ball diff personally, but you can get a similar effect by building the standard diff with a thick grease or even blu-tack on the internal gears.
David Allen - www.digitrc.co.uk - Xevo - Much-More Racing UK