Re: New to motorized bikes
Definitely keep your first build simple as possible.... then as you learn these things you can better decide how to get more out of the bike. If you need more hill climb ability or if you want more speed, both these can be accomplished while keeping the bike a simple single speed bike either by changing sprockets to get more speed or better hill climb, or by keeping the stock rear sprocket and doing the necessary upgrades to get the speed you're looking for or the climbing power. My first build was topping out at around 28mph, then it got faster as the engine broke in. I did some port work, added a Fred head, then made up a pipe for it and the bike was topping out at 43mph with plenty enough down low to climb hills if needed.
Adding a jack shaft so you can use the gears is also a good way to get better acceleration, climb, and speed while keeping the engine stock or close to stock, but doing the build first, then as you break in the engine and all you will have the time to read up in here and ask questions to get a better idea of how you want to set your bike up and which method is best for you and your budget. The more you learn about these things, the easier it will be to decide which way to go and get the results you want.