Any bike that falls into my hands always gets the motor seen to first.
That way I know what I'm facing $$ wise in the near future, if I can get her to run right and strong all good and I can concentraite on the other bits (brakes are a good thing as now its running you will need to stop it).
I like to put new tires on if they need it so I'm wheeling around a decent rolling frame.
All the rest just falls into place, if the motor is coozed then while I'm waiting for parts or funds I can work on the free stuff like cleaning and prep.