We are currently in the same situation as you are, only a couple weeks ahead.  Our 7 year old Rottie got the same diagnosis 2 weeks ago today but on his rear leg.  He woke up limping Sunday morning, we immediately took him to vet next day and after X Rays we got the terrible news. Thankfully his body scans came back negative for spread so as hard as it was to wrap our heads around it...we immediately moved toward amputation.  

He had surgery four days ago and walked out of the hospital 24 hours later.  We are keeping him quiet and his activity very low and confined but he has made tremendous strides already.  He is about 95 pounds with an athletic build.  It's three days after surgery and he can already get up on his own and move around pretty good.  It's really quite amazing.  He's like, "Whatever... I guess I'll just hop around from now on."  

He was a little wobbly the first two days so we used a harness and leash to keep him steady but today he is getting the hang of it and doesn't even need our help stabilizing himself when he's up.  He seems to want to move about more but we are forcing him to go slow and are keeping his moving sessions to just a few minutes at a time followed by hours of rest and an ice session.  He is peeing but we are still waiting for that elusive first poop.  We are cautiously optimistic and know there is still a long road ahead to recovery but so far so good.  

I don't know Tank or what kind of shape he is in now but I hope our limited experience thus far helps.  I was apprehensive of posting this because things can just as easily change for the worse at any moment but reading other people's posts have helped us out.  Our advise is to just concentrate on one task at a time as you move forward.  Your next step is body scans so just focus in on that and then move forward to the next thing after that otherwise it's just too overwhelming. 

My guess is Tank will handle it like a champ...after all, he is a Rottie!