Perhaps a large hole for inlet to booth. You can use those cheap 1" furnace filters. You don't want it to be too restrictive. Large hole so you don't get a noticeable breeze. Best to have garage door closed to control the temp. What temp will you be spray at? I found 70F ideal. Make sure compressor is drawing in air from a clean source and around 70F. I don't know what your temps are there but don't let the booth get cold before or after as you might get condensation on the ceiling. A good stable clean air environment will ensure the paint flashes over properly with no sags etc. I'm a self taught painter, learned the hard way! Painting your own car is VERY gratifying work.