Thoughts on Duracoating? Anything will help

[Misery Loves Shotguns]

Long story short, I saw a video on youtube of a Remington 870 that had been refinished in a matte black and now I want to do mine. I've already sanded it down to a mirror finish and I've been keeping it oiled so it doesn't rust in the meantime. Is the shotgun being super polished going to affect how the duracoat turns out? How much do I need for the reciever, 18.5" barrel and magazine tube extension? Should 4 ounces work or do I need the 8 ounce bottle? I know that I'm supposed to degrease it before and then let it sit for a few days before reassembling it, any other bits of advice? I've never done anything like this before so I know it isn't going to be perfect but I'd like to be well informed so I don't totally F it up.