I'm glad it helped and wasn't confusing.
yes, your right in your thinking the cage is to small. When cages are to small they can cause some depression. Signs of stress or depression are
overgrooming (bald patches of fur in various places )
Stress circles, the glider will do back flips in one spot for an extended amount of time. And or run in circles around the top of the cage.
Any habitual behavior can be signs of stress or depression.
A bigger cage and stimulating toys and a cage mate can help to relieve depression/stress.
36 inches high x 22 inches deep x 33 inches wide is a good minimal sized cage for one or two gliders at the most. The one you currently have would be a good hospital cage or travel/transport cage.
There are few really good quality cages out there that are reasonably priced. Brisbane goes for about 130$ to give you an idea and is the dimensions I mentioned above.
I am sooo glad you removed what ever wheel that was ty! Most commercial wheels you find in pet stores are not glider safe. Commercial wheels are designed with rodents in mind, gliders do not run like rodents and need a wheel designed for their natural hopping leaping and jumping motions. Glider safe wheels are only found online and there are a few widely used wheels
http://customchoicecruiser.all4gliders.com/
http://atticworx.com/
There is another one but orders are backed up atm due to the makers health issues so I won't give you that link
Toys.... Pleaseeeeeeeeee be careful with branches some wood is toxic to gliders, wood is also porous and absorbs urine and won't take long to start smelling badly.
Fleece is really the only "safe" material that should be inside a cage. Though some hammocks are ok depending on the material.
Easter eggs, drinking straws, baby toys like rattles, plastic bracelets that are big enough they won't get stuck in.....
There are tonssssssss of toys that are cheap that can be found at dollar stores, even toddler floor toys can be used as long as any holes are larger than 2 inches.
Braided fleece for them to undo helps to stimulate their mine. The easter eggs you can put treats in to use as a foraging toy... use your imagination and feel free to look at my pics and other member pics here to get some ideas on what to put in your cage.
Cagemate....
Age is really just a personal choice, but you want to try to find a glider about the same size as your current one. So if they fight during introduction neither have a size advantage. Having said that I have a male that is twice the size and 3 yrs older than my female and they introduced just fine.
male vs female.... as long as your current male is neutered either gender is fine.
If your male is intact he will need neutered before you introduce him to either a male OR female. With a female he would breed. With another male they will likely fight.
So it's best if when introducing 2 males that they are both neutered and have a waiting period for the hormone levels to drop before trying to put them together.