There's some real pros here on that topic so I'll leave that for others to jump in on.

Should I try to rerent the place out or do I have to leave it for a while since I did not get the keys back or a written notice?

Do not call and leave a message.

I learned from the owner's mistakes and I plan to create a system/business that I can teach to one of our tenants before we leave, based on the knowledge I've gained here in BP and elsewhere.Is it reasonable to think I can find 100% financing, whether through sub2 or some other means?

This is purely personal preference, but I'd probably wait 6 months before raising any rent, and then just do it one tenant at a time (based on their renewal date or something) so if they do leave, you won't be faced with 4 vacancies :) Also - I would find out how much you can really get for rent from these places (maybe place some "test ads" on craigslist and see who calls, and look for comps, as you have.)Good luck!

She was breeding dogs there, I suspect illegally, and would sometimes leave for the weekend and it would sound like the dog shelter in her back yard.

IN this case I was 95% certain she would leave, which she did.

That's a good thing leaving the 100k open for future advances.

We live in a big city and I'm not going to drive a beater that might leave me on the side of the road.

Been reading the books and dragging my feet for years while I established my professional career (love it, not looking to leave, just supplement).So I live in a nice college town where occupancy rates are high and the leases run 12 mos. and I'm ready to get into the game.