As you know, we have a combined household of 4 intact GSDs and two "other breeds" that are fixed. 3 intact males bred for Schutzund and an intact female for same...aka strong temperaments.
I have found Limit does best OFF leash with the new dog on leash so that he can escape when needed. Otherwise, with all the GSDs we did a lot of crating near each other, and on and off leash time while we each kept our dogs engaged. I realize that will be harder for you since they will both be your dogs. But, if you have a friend that can walk with you or something, that makes things easier.
I like the 2 week shutdown.
Don't baby Trent if he's being a dick (same with the new girl, no matter if she's new). Lay down the rules right off the bat and stick with them. If they're both strong tempered, confident, pushy dogs (like mine), then being sweet with them in terms of rules will just cause confusion. We are extremely strict and very very clear with expectations.
Some examples of rules in our house that lets them live happily together:
No stealing toys from others. Whoever has it first, gets to keep it until they leave it alone.
No posturing, period.
Anyone that starts anything, gets punished, immediately. For a time Kas would start crap with Lim and then they'd both go at it - they were both punished. Now when one gets over-stimulated, they look for other ways to release the pressure rather than reacting to each other.
No pushing me, no rushing me to the door, no slamming each other around trying to get in/out/or through doors.
No neck biting in play. Bones LOVES to do this, Jentry doesn't mind it - it sends Limit and Kastle off the deep end, he's discouraged from doing it.
Everyone gets left alone while pottying (sounds silly but dang can other dogs be rude when one is trying to go potty - especially with boy/girl dynamics).
The male GSDs have STELLAR down commands. If things are getting too rowdy (we potty all of them loose together and when we first get home from work that means a lot of excitement), we yell PLATZ and the three boy GSDs will drop, usually Limit will recall - and then we can get a handle on the two naughty girls.
I 100% agree with what Danielle said about gates..and be aware, doorways or toys/beds tucked in corners may be looked at the same way. As guardable.
I adore having multiples, can't imagine life without it. So fun. Always someone to do things with - no matter what it is I want to do. I also enjoy "teaching" a dog something by using another dog to show it. Lots of fun.