You bring value people come to you. It does not matter what kinds of value. Often one partner brings the money/credit and another is a contractor. Maybe a third partner brings the properties cheap. If you have done some sorta business venture outside of real estate with someone such people often make good partners. You know who your getting in bed with. Sit down and figure out where your value added is and what kind of partner would compliment that.
As for rehab costs.
J. scott's book on running rehab numbers is decent. Basically you see the home as a set of main systems (plumbing, hvac, roof, electrical, even drywall), finish levels (how high end will you go on each system) and fixtures - pay close attention to little stuff like faucets on the fixtures. It adds up if you buy retail. J. Scott's book helps but it's all experience and not finding a major surprise behind a wall, like a ruptured main line or something.
Final piece of advise, leverage any small tight nit community you happen to be a member of. Be that family, church or a book club you have been a member of for 20 years.
PS get some negotiation skills asap
And run the numbers on a deal 5 times before buying.