If you just want to test the waters a bit without a lot of investment, you might try installing customer's lights for a season. There are plenty of people looking for someone to hang their lights. I turned down a ton of calls asking for that last season.
You will have very little investment and no long term obligation. If you like the business, do it right the next season, if not, just don't offer the service again.
I would stay away from selling discount store lights.
Whatever you do, definitely take time and go back several years and read the threads on this forum. Several years back there was a guy named DeepGreen I think who asked a ton of good questions. David, Hotrod and Hokie patiently gave a ton of great answers. Definitely find those threads.