I doubt that any amount of add-on parts will be a problem for that clutch. When you start boring the cylinder, increasing the compression ratio, porting the head, etc then we can revisit the clutch situation.
As far as the comparison between a big block and a Rotax, I have years of experience building and road racing both. Without doubt, and by the greatest superlative in the English language the Rotax is the king of reliability, ease of maintenance and greatest interval between rebuilds between the two.
I've built plenty of engines with a billet flywheel, hard starting vs stock flywheel is news to me. Others may chime in on that issue.