light leaks like you mention, under the door, are NFG. You must prevent this. There can be a light baffle where air can enter but light is 'trapped'. Though under the door is a challenging place for this. Maybe a dark fabric skirt fastened to the bottom of the door?
Smell in the working part of your house will be an issue at some point. If one can't exhaust the air outdoors to a safe location then exhaust fan and charcoal filtering is used.