@Alex T. First off congratulations on your first purchase. Its the right step towards gaining success in RE.
To begin with, BE READY FOR BAD DAYS, DIFFICULT DAYS, DAYS WHEN THINGS MIGHT NOT GO YOUR WAY, and tell yourself that's fine, that's your learning curve and you will get through this.
Now the rehab:
Start with checking the plumbing for the house, electrical work and also your HVAC/heating systems.
Fixing or upgrading these things mean breaking walls and you don't want to do that later. You cannot live in a house if the above three things are not working but you can live in an un-painted house with broken walls if the above three are working.
Make sure you give enough closet space, that is the most important piece in any bedroom.
Roof - you didnt mention how much repairs are needed.
most important, decisions about paint color, granite top, kitchen cabinets tiles in bathroom, don't kill yourself in making those choices, be smart and quick, don't look at 100 designs to make a choice.
Associate with a few realtors in the neighborhood to get an idea of what other buyers look for in that town.
Thanks
Kunal M.