Sounds like you should of asked a bunch of these questions before you purchased this engine. IMO your cylinder will not be a 2009 or newer based on all the other changes needed.
If your club racing chances are you wont need to make all these changes for club racing. If you plan on doing more than club racing you will need the updates. Check your local track rules on Rotax.
By the time you do all this to this engine it will be close to 2K with parts and labor.
A cylinder is close to $700, clutch kit $500, airbox around $70, new piston for new cylinder $150, plus all the gaskets, bearings and other parts needed to complete with seal and labor.
I would sell engine and get a newer engine. What ever you decide to do, Rotax is still a better investment than the other Tag engines.