1. he might play all of those positions, but i doubt it. he'll need to rest eventually. and he won't get very good training time unless you're doing team training, which i wouldn't recommend for an extended period of time.
2. too many minutes is over 90 minutes in a week.
3. buzzerbeater is alright in suggesting positions, but you don't have to follow them. lots of users have players that are suggested small forwards, but play them at point guard. in your case you should know that shooting guards are measured more by jump shot, jump range, driving. passing is important but the other skills are better since a shooting guard will take more shots. if his inside skills are not bad for his age then you can probably train him more at the inside positions.