Welcome Marcia,
Wow, you've done a whole lot of reading. Would you settle for....
. I am sure people here will be happy to share dimensions. Ask your questions here.
Here are my thoughts.
With a human companion, four cats and two parrots in a cage, consider a 2552 or 3100. If you decide to buy a brand new PC, the factory may be able to accomodate a special place for your bird cage between the entry door and passenger seat, and kitty potties under the cage. You might also consider having the front aerodynamic cap finished "open" as a loft for the kitties to hang out. You could later create within the loft, a multi-level kitty loft if your kitties need more personal space. I've heard the factory can make that area a single bunk for a large child. They don't cut the roof of the van, making it quite a nice open space area. Of coarse the TV goes elsewhere and you loose those two side cabinets. You also would need to watch your head getting in and out from the front seats as is common with other motor homes.
I do wonder if the TV could still go there, just let the kitties claim the space behind it.
I also wonder if a slideout would help or hurt with kitty access to the loft. Someone with those PC models would have to provide input on that.
Blessings,
Ron Dittmer