Just leave it alone! All that build-up inside is the sign of a "well seasoned" smoker. It's not hurting anything. If you're worried about bacteria, just turn on the smoker 30 minutes to an hour before you use it. The only thing that needs cleaning is the racks.
imo off course!
I just wipe it down every few times with a towel on the inside- you don't need or want it "new". That knocks off the biggest blobs and so would eliminate anything that could start molding up if I ever gave it the time to do that. If you chemically cleaned it you would need to season it again and that would get the smoke back on the walls.
I clean the shelves that I use every time I use them; if I'm not using them I'll take them out. I empty my water pan every time to keep the mold from starting and the tastes "fresh", and change the foil I line it with top and bottom about once a week (2-4 smokes). The bottom drip pan I also have lined with foil except for the hole, and change it when I'm made a big mess on it. The wood chip pan I'll just take and toss it into the yard before I start a new smoke. The outside gets spray stainless cleaner about once/week.
Pretty much do the same as smokeguy. Never clean the walls or door. Clean the shelves after each use. I use Dawn Power Dissolver to clean the shelves. Also no reason to have a shelf in there if there is nothing on it. Water pan is cleaned after use and is lined with heavy duty foil. Drip pan is lined with heavy duty foil but has yet seen much in the way of drips since most falls into the water pan. The door gasket may need a little clean up and lubrication to keep the rubber soft and pliable.