Welcome to the best motorized bicycle forum on the web! In addition to all the great mechanical advice you will find here keep in mind a few lifesaving details.
1: You are almost invisible to many motorists, they do not see you on your bicycle and definitely are not watching for you at 20 - 25 mph.
2: Any other motor vehicle outweighs you by hundreds or even thousands of pounds. You are the automatic loser in any collision.
3: Wear a DOT approved helmet. It may be hot, inconvenient or less than 'cool' looking; but you don't want to ever chance meeting the pavement without one.
4: None of us are invincible, even though we all felt we were at 16. Drive defensively and slower than you think is necessary. You will still be enjoying the ride decades later.
Sorry if I sound like the old fogey in the bunch, I've been riding motorcycles since I was 15 (now 60) and I want you to enjoy the ride as long as I have or longer.