The gear depends on what you're doing. If you want to pick up wheelies on the highway and go for miles then 2nd maybe third depending on how fast you want to be going. If you want to do slow shit i.e. 12's, no handers, etc. then first gear. And as for how long it takes to learn stand ups is really subjective, it may take some people years, it may take some people a couple weeks. It's all in your self confidence and not worrying about dropping the bike or getting hurt.