Just bought the wife a new bike, so I have stole her old L2 ZXR400 for my track bike (much to her disgust

and I would like to go racing at some point just for a bit of fun,I'm going to do some track days to set the bike up, get used to it and so forth (I've got a van as well and the bike will not be used on the road at all).
Basically I'm going to use this year to get it setup, take it nice and slowly as a project, not sure what series to go for, but does anyone have any basic recommendations for general mods to do that will be allowed in most clubs, I've read the BMCRC Formula 400 2009 technical specifications, it seems the frame, swinging arm must all stay standard, but I can change brakes and so forth?
i.e tyre sizes, brake and suspension mods, general things to remove, what catch tanks would i need and so forth etc...
What I've got planned so far is to get race body work, remove any unwanted electrical parts and remove the wiring from the loom and remove any unwanted
bits and pieces, junk all the clocks and stuff.
I've looked though every page in the racing section here, and get a general feel for things, but still non the wiser for where to start,
Any help would be appreciated.
Thanks in advance
Mark