Welcome! I've been boarding out of our home as a hobby for the past 10 years, but I decided to try and turn it into a business last year.
I've been blessed to have a very positive experience...both with the dogs and their humans. ;)
Damages have been incredibly minimal. There have been some housetraining accidents (everything single one of which has contributed to my anti-carpet stance), a few scratches on our kitchen table from a counter surfing dog, a few teeth marks in a measuring cup, and one chewed through leash. The biggest damage happened 7ish years ago and was, unfortunately, recently repeated: a set of faux wood blinds.
Outside of Rover, I foster trained a dog for three months and he chewed through a seatbelt, pulled off a tiny piece of car upholstery, and ripped a hole in my bed skirt. I really don't consider him a regular boarder though.
When I did this as a hobby, I sat maybe once a month, or once every other month. In the year since I started advertising more, I've been incredibly busy---272 booked days from September 2014 to September 2015. My average stay is about five nights, and weekends/holidays fill fast. I do have some regulars, but I always love getting new clients.
As a hobbiest, my prices were laughably low. I've raised them considerably in the last year, and plan to continue. It's not just the fact that I want to earn more money, it's that the busier I get, the more work it becomes. Running it like a business takes time, and I can't afford not to be compensated for it.
I do not currently offer a doggy day care. I'm not confident mixing unfamiliar dogs with each other, plus I work an 11 hour shift two days a week, so it just doesn't work for me. I think you really have to have the right set-up for it. Even if I had more knowledge and didn't work the hours I do, I'm not sure our house would be good for it. It's tough to live in the same place dogs are rough housing in.
I wrote up an article as kind of a "Things I've Learned and Advice I'd Give..." piece. If I can figure out how to get it to you, you're than welcome to read it if you'd like.