welcome dude
first off im probobly not the best person to help you out with most of your questions as i am still learning myself but...
1. 15 isnt too young to start out
2. again it isnt too young, start off with a whey protein, creatine, flax seed oil, bcaa's, multi vitamins
3. not really the guy to talk to on this one, i do split workout, say monday i will do chest and triceps, tuesday back n biceps ect.. but you must include cardio
4. again im not really the guy to talk to cause u said ur on the chubby, dont go overboard with the carbs and try and get in a gram of protein for every pound you weigh.
5. dont listen to black eyed
peas, you should listen to metal, gets you pumped and its the best for training lol mygeeto
also mate u should have done this in introduce yourself