the first question I would aak would be to you: What level competence do you have to install, rehab and repair such a house? If your asnwer is none, I would question the size of your checking account.
You will want to the major factors already updated or at least in good working order. This means, from the top down, the roof covering, the house wiring, the plumbing, any HVAC system and the foundation. If any of those need immediate repair, and you don't have the knowledge, get more money. Anything else can be tackled in your spare time with money carefully doled out. But a roof could cost a few thousand, as could the wiring and plumbing, while the heating and cooking and foundation repair could run substantially more than that.
Then again, if the windows need to be replaced, figure a couple hundred for each of them. Siding will costs thousands, sidewalks and driveways, thousand, etc. If you have to pay for a ll maintenance repairs, it is generally prohibitively expensive