Well it's good that you found out hamster/gerbil food isn't good for them, However neither are glider pellets. At least they aren't good for their main diet, eating them for a long period of time can cause "lumpy jaw" and their fur to turn a brownish color when it should be grey. Giving them pellets as a snack is ok I believe a couple pellets here an there are good for their teeth.
But overall gliders
NEED a nectar like staple for their main diet. Along with a variety of fruits and vegetables. There are many "approved" diets here to choose from, a member named Candy has a lot more knowledge and diet information than I do on hand. This food should be left in the cage over night and removed in the morning. Most of the time gliders don't wake up during the day for a snack on their own. They will wake up however and may need a snack in the bonding bag during the day.
It's great that he has a wheel, but considering they had you feeding him hamster food I'm a little worried the wheel he has may not be glider safe. Some hamster/gerbil wheels have led to a lot of injuries, broken tails and even deaths for sugar gliders. It would be helpful if you could post some pictures of whats in his cage.
Cedar is not good for them no, there are some safe woods but pine and cedar are not on the safe list. I don't use any type of bedding in my cage, gliders don't really need it and if they drop food then pick it up to eat it they may ingest the shredded bedding... For me it's easier to just skip bedding and tray liners and simply wipe the tray every day with a mild soap and vinegar mixture. That being said, my local rescue uses a crushed walnut shell bedding for her glider cages I believe she found it at petco. She has many cages to tend to where I only have the one so for her bedding is easier than wiping the trays everyday.
The smell.... is your glider intact? or has he been neutered? If he is intact he may have a very strong pungent odor. Getting him neutered will remove most of that odor! When they're neutered the scent gland on top of their will begin to "dry" up, his over smell will get better. Intact males will "mark" everything in their cage to make it all smell "like home" and to let others know he is the dominant male of that territory.
His bedding and fleece things probably did indeed need a good washing. But keep in mind "over cleaning" things in their cage can make an intact male "mark" everything even more to get his scent back on it. Best to use mild smelling or no scent soaps on bedding and pouches to prevent over marking.
Some other
Important things to do is find a glider experienced vet in your area. Gliders can hide illnesses very well and considering he hasn't the best diet for 2 years you may want to take him in for a wellness check.
Nail clipping probably needs to be done as well. If his nails are to long he will get snagged and stuck on fleece etc potentially causing nail or toe injuries or worse.
Then of course you should really consider getting him a cage mate. Gliders thrive the best when they are at least in pairs. They can become lonely, depressed and even over groom and self mutilate. They are colony animals and should not live solitary lives, they need interaction with at least one other glider friend.
So far you've made some good adjustments to his living conditions, just a few more tweaks here an there and he should do very well. Your doing a good job, and keep up the research
how big is his cage??