If he was running race fuel, it might need it. Easy way to check is do a compression check. Anything over 150ish then you need higher octane than pump gas. But if the stock head wasnt milled or other things, i doubt that.
I run my oil at 40:1. But everyone has it's own opinions on that. Amsoil will be ok. I used to run that but the lack of caster oil made me switch. I love the smell of it.
Stock gearing will be fine. Or if you ride sand, maybe go one smaller in the front. As long as it revs crisp in neutral and 1/4 throttle to 3/4 is crisp and good, your needle clip should be ok. You can always go one clip richer and see if it bogs.
With just a boost bottle, you will not be keeping up with any of today's bikes. Actually boost bottles does nothing. Over time from bouncing on the rubber boots, they can cause the rubber boots on the carbs where it attaches to crack. Just make sure she is jetted/tune right and enjoy her as is. Welcome aboard!