To change a light bulb?
Just one, Trekkies are no different from anyone else, unless of course they are physically impaired, then, if attempting to change a light bulb they should ask for assistance from another person.... preferably able bodied.
To Move a Grand Piano?
Depends on the size of the piano and where it is going to be moved to. I would suggest 4 is a good number for most situation.
To sexually gratify a small dog?
None. This is an illegal activity in most places (not in Ireland where it is actually encouraged)therefore any person, Trekkie or not, would face the full consequences of the law and of course the Federation if they touch ANY animal inappropriately. This includes bribing the dog with the reward of licking "Bones".