Nice bike! She's a cutie.
I wouldn't worry too much about the tach drive as long as it's not leaking any earl. As long as it stays in place there's no need to worry much being that it's not a critical saftey issue.
Things you should do to make it road worthy:
Replace the tires. Even if they look like they have tread left, they probaby have dry rot and won't be as soft and grippy as new ones.
Give her a tune-up. Oil, filters, points, etc.
I'd rebuild the front master cylinder as a matter of course. See the thread on rebuilding the caliper and master cylinder on this forum. It'll run you about $40. Money well spent.
check the chain tension. Also, lube it up.
Check the cam chain tension.
There are other things as well, but start with those and use common sense.
Finally, Old Navy flip-flops aren't the best footwear for motorcycling. Birkenstock clogs are a little better, but not by much.