advice for modifying a razor e200

[kearns_hippy]

Hi! I bought a Razor E200 for a couple bucks last week, and decided it would make a fun project. The rear sprocket and batteries need to be replaced, but everything else seems ok. I've never built an electric scooter, although I do understand the basic parts (battery, motor, controller, etc). What I'd like to do is get a 20 mile range (mostly flat terrain) and be able to go up hills easier (without having to assist). Is that possible or a unrealistic expectations?
Also, what options do I have for the battery? I can solder, but am not an electronics guru. I've seen people on youtube and reading on here that use the 18650 batteries to make a pack. What kind of advantages and disadvantages are there?
Thanks so much for the help!