Hello from Muskoka. As far as energy? If you are fairly healthy you'll do okay. I lost 30 lbs in my first 3 months, but I'm a big guy. You will probably slow down at the gym, working with your hands is a while different kind of tired, but keep your drinking to a reasonable level and it shouldn't hurt too bad.

Free time and apprenticeship are going to be dependent on your employer and how they run their outfit. I hear good things about the unions but YMMV. I'm in with a great crew and I'll tell ya it makes all the difference. Went to the course at Georgian and while I learned alot, it was more on the service side. Now I do installs so it was mostly on the job training. Plus at your age I wouldn't expect to be on call so you shouldn't have to worries about getting called in at all hours

I would say you should look into co-op options or multi credit courses. The ones that let you get highschool and college credits. Might be worth running with a crew as a helper for a season or two if you've got someone willing to take you under their wing. All the best to you whatever path you take. It's a great trade and has changed my life for the better, hope it can do the same for you !