They definitely have to be overwintered based on your location and that they need about another month till release. I’ll do my best to answer your questions.
1. I’m not sure about the cage being outside. I live in Florida, but others that live in your area will certainly be able to advise you.
2. Size difference is normal as long as they act healthy. No, you shouldn’t have to separate them unless you see bullying going on. A larger enclosure is ideal. Maybe even provide a couple of cubes and nest boxes inside the enclosure.
3. If they are eating the Zupreem and not stashing it, then all is good. Remember nuts need to be kept to a minimum. As a rule I don’t give any nuts till they go to the release cage. That way I don’t have to deal with the squabbling or nut aggression. For a treat substitute a little chunk of Henrys hazelnut or peanut stix, a clump of granola, a piece of rice Chex or Quaker Oatmeal Square cereal, etc.
4. Wooden hanging bird toys. The small ones get whittled down pretty quickly, but it keeps them occupied.
The larger ones are good, too, bird toys that incorporate jute will be happily shredded, stuffed toys that are on bungee type cords and hung from the cage, a box of tissues or roll of toilet paper (they’ll line their nest box or cube with it), a treat listed above put inside a toilet paper tube with the ends taped shut will provide entertainment as they chew it open to get to the treat.
5. We built our release cage in panels. Each 4x6 foot wooden frame is covered with hardware cloth then assembled together. My release cage has a vestibule that I can walk into and close the door behind me before I open the door where the squirrels are. Assemble the cage with the wire on the inside so they can’t access the wood to chew. I’ll attach a picture below. Our floor is hardware cloth so droppings fall through. If you are going to use this cage on your patio you could put a heavy duty tarp or shower curtain under it to catch the mess. Then because it’s in panels it’s simple to disassemble and relocate the cage outside and use it for a release cage. This release cage picture is one we built around a tree. It’s a little more complicated, but can be done.
6. I will attach a picture of the nest boxes we make. They need a predator guard for sure. If you’re interested send me your email in a private message and I’ll send you our nest box plans.