Here is a list of of what to expect with different motor/battery types.
Click on picture:
Unless you are a pretty hard core tinkerer with electronics, you are not going to want to get Lipo (that is definitely not plug and play). Lithium ION, or better yet LiFePO is a lot safer and easier to work with for most people.
I'm not sure why anyone (other than the electronics tinkerers) would get LiPo unless they want a very large pack and don't mind the complexity of wiring things in parallel and series, tracking the status of each battery individually, and the safety/fire issues. That is a lot of caveats. They are great for the hard core guys who like that kind of thing.
Battery is your biggest expense and is going to determine how fast you go (24 vs 36 vs 48 volts) how much you spend, and how much your rig weighs. As you can see, it is pretty hard to go over 20mph with 36volts. 24 volts is good for riding at slow speeds indoors (or maybe just for slow speed hill climbing).