I can only really help with what isn’t worth doing… the waymarked 10 Under the Ben route is pish. (it’s also quite different to the race routes) Don’t write it off entirely, you can work the fun bits into a lap of the Witches with just a little fireroad bashing, but definately don’t do the whole thing- total waste of time and leg.
Can’t really recommend natural rides round there- we did a nice loop out of fort william, down glen nevis along the Way as far as the military road then back up on the tarmac, and round cow hill- pleasant but nothing amazing tbh.