Welcome to the forums!
Just a bit of advice, someone will chime in if I'm wrong. I'm only 17, "I don't know much". But If you only have 8 lawns right now, how much time does it take? 4 or 5 hours? Lets say you want to have 15, at about 35 minutes a piece, Roughly 9 hours. Nice and easy to spread out over 5 or 6 days. "Too much" is when you're working 40 hours a week, and then some overtime. Don't get me wrong, it's great money if you can go at it like some of those people. But I'd say go for 15 next year, try a few bi-weekly or one time mowings mixed in, if you can handle it, go all in. It's just a matter of what YOU can do. Just keep in mind, NEVER do more than you and only you can handle. Learned that this year when I hired someone, and they just stopped working. Experiment, see what works. You'd be surprised at what works sometimes.