you have quite a few options that dont have to be "undone" when selling your house.
Do you have a double garage door and a single garage door on your 3-car garage?
Install a partition between the 2-car section and the 1-car section.
Is your garage currently drywalled?
Cheap commercial carpetting will help decrease the dust and help to insulate. And it wont interfere with future parking requirements.
There is only a requirement for "covered 2 cars parking". The third parking spot is a selling bonus...but so is a bonus "man-room".
In any event, as long as the garage doors remain operational and the required parking is satisifed, you can make your garage do what
you want it to do...for not a lot of money in materials.