1. County record has deed, mortgage, lis penden information, transactions of last 30 years and more. City has tax, water bills due and paid. For house for sale listing, check trulia. You also need a good agent who knows the rental market, at least from the beginning. Current rental market you can check rental listings, and talk to people on the street (this is important, because if you have never lived in inner city, you don't have a clue what you see, and you might end up owning a drug house). At my place these info. are all on-line for free, at your location you might need more effort.
2. For old house, be prepared to have a plentiful repair budget. You will find out the money ended in you pocket is not as much as what they tell you.
Got a leaky kitchen sink to fix today.
Good luck.