the biggest question to ask yourself is "Am I doing the mission or will I have someone else do them?" If your going to have someone else do them you can just as easy Download a 100% completed game.
That's right.The internet is full of 100% saves.I've started playing San Andreas from the beggining,and I'm going for 100%,so I won't have to always ask someone to do them.AND with no cheats.I think it takes a long time,since it's my first time going for 100%,but it's fun,you should try it out.
Once you have completed the Game, it's time to go back and keep at the bits you have had trouble with. Once you can do all the missions then you can go for the 100% on your own. For practice download the "Mission Help" of a mssion that you had trouble to work on that specivic mission without having to go through the whole game. then you can do the whole Game. You have about 30 days before the saves become inactive.
No at all. Once the game registers the School completed that's all you need. Not Spawning of any Prize Vehicle is common, usually just driving around the block will bring them back. I have only seen them all spawn Once in a Chain Game. Completing the school is all that is important for 100% the Gold is Not required in any of them.