This is one of those questions where if you ask 3 people, you'll get 4 answers but i'll give it a go. As far as headlight repair goes it's a fairly simple thing to do. Don't fall for the wipe on wipe off stuff you see. It will never work. At the present time I use a metabo dual action sander with a 3 inch pad and sand paper. I use 400, 600, 1000, and 2000 grit paper. You can polish the light after sanding with compound and a small foam or wool pad if desired. I quit polishing because I was having problems with my clear coming off. At the present time I use the Dvelup clear wipe for the protection.
With windshield repair it is a little more of a learning curve than headlights. Most of the people selling the professional kits will provide
training with purchase of the kit. You can learn without
training, but if possible I would do the
training. Lots of little things that come up and tips and tricks you can pick up on. I use Delta Kits and several of my friends use Liquid Resins. I like Delta and haven't had any problems with the equipment. They also sell headlight repair supplies. Sorry for such a long post but hope this helps.