For the door, teach him to ring bells. Be forewarned: he may go through a stage where he rings them constantly just b/c he can. You have to open the door each time. Of course, you can just refuse to let him back out if he starts doing the in-and-out thing, unless he is already trained to let you know he needs to go out to potty. Then you have to let him out every time he asks, and have to let him in every time he lasts. I couldn't hold steady in this stage; my dog rang the bell 5-10 times in an hour for a few days after he learned, and I gave up. He "asks" to go out by waiting at the door, but it's not as fun without the bells so it's a lot less often now.
As for chewing, I'd say just don't leave him unattended. Young dogs like to chew and are easily bored. I don't care how many toys you leave; chances are, if you leave him unattended, he will find the one thing he is not supposed to chew and will give it a go. "Experimentation" is common to teens, after all.
Radar, Aussie/BC mix, b. 2/27/2012
Jett, GSD foster pup, b. 7/15/2018