Sorry to hear about your woes and still kinda happy that you are in the place your are in. I see opportunities. You will too soon I'll bet.
I see the opportunity to breathe, ponder, get organized, breathe some more, ponder some more, and face your true feelings after the move and emotions you've been thru. Get what you can...no REALLY WANT in the 20 long. Wish you could do a longer temp tank, but if 20 is the limit, OK.
As far as the live rock, I used large, hard plastic tubs. Circular ones with rope handles on 2 sides from Lowes or Home Depot. Maybe you can use a trashcan, depending on the amount of rock. Put the rocks in there and added a powerhead 24/7. Depending on where you keep it - my ambient basement temp in my water was about 74 or so - so I didn't add a heater. You may need to. Added a pinch of food every 3 or so days with no light to keep the bacteria feed. Re-set up my tank 2 months later maybe and all was fine. Even had mushrooms on the rock that came back after it got light again.
So, as you breathe for a bit, you'll decide if you want to do it large again or not. And if you do, you will have come up with so many neat and functional new ideas for the next setup, it'll make you proud of the planning you did. And it'll all work better next time too. Anyway, I see opportunity. Just breathe awhile.
Good luck!