Welcome to the board...great place for help here. I'm assuming you got out the old gas, changed all the fluids (especially the brake fluid) & changed the plugs.
Since it sat that long I'd figure you had some water in the system. Change the fuel filter, get the injectors cleaned professionally. Maybe flush the tank with dry gas, then run some Techron or Sea Foam through it (Sea Foam can do oil, gas & intake cleaning, just Google it).
Then get it inspected by a local independent. I'm sure you can get some good suggestions from board members here. No matter how good you think you are, a seasoned BMW pro will absolutely have some tips & suggestions. It'll be the wisest money you spend, and remember that these cars can be absolute money pits. You're lucky that you know the car's history!
Post some pics in the member section too, we'd love to see your car - regardless of condition!