Hey, welcome to smoking addicts.Wish you all the luck in the world, its not hard just a time learning curve. I have been smoking all kinds of meat and veggies for 40 years. I in your question about the door size, make as large as possible with a lip inside to help prevent as much smoke escaping as you can. it's hard to do with home made smokers but the bottom edge about 1 inch above your bottom rack, belive me you will be glad you did.I'm including 3 articles and email address to this smokers regular emails. These are 3 steps to smoking a whole pig. They also manufacture a variety of large smokers like you are going to build. Good luck and have fun, smoking is addictive. PS you will need to go to the email to get the 3 steps. I didn't have your email or would have forwarded them.