When I was 16, many years ago, I bought an old beat up sears moped (hence my handle) and repainted it as a do-it-yourself project. I used rustoleum spray paint, and achieved acceptable results. I still own the bike, and 20 years later it still looks presentable, even though it hasn't run in a while.
Whether you need a manual to disassemble depends on your experience. Most things can be taken off (like the engine) without further disassembly, so you just need to remember where things go to put it back on. Photo's taken during disassembly can be VERY usefull if memory fails. Also you can mask off things which you don't want to paint using masking tape and paper or plastic bags.
The amount of difficulty you will encounter depends on how good a job you want to do. A half hearted spray over can be done in an afternoon, and it will look like it. The home mechanic can do a very good paint job in about a week that will be difficult to tell from a factory job at a distance .
Hints: don't try to get it all at once, thin even coats look the best. If the original color shows through, it just means you need another coat. Let the paint dry completely between coats. at least three coats will be called for.
you don't have to sand and prime, I didn't. DO be sure to wash and dry thoroughly, and sand any rust spots. I'm not the best painter in the world but I was happy with what I did. If you want a top notch job that will look at least as good as factory or better, you may want to ignore my info, and find someone who REALLY knows paint! Good luck!