For one thing your rust colored paint is an epoxy liner. If your fire laws permit open burning then probably half or a little more should do a pretty good job. I won't say that 4 intake holes is overkill, but depending on the exhaust ports you use, three should be adequate. Don't take what I have said here as absolute, you should get more feedback and continue reading the threads. You might want to keep notes with page numbers so that as you gather info you can sort of keep score and the number of pros and cons to the many building options you will face.
HAPPY building - keep it fun!