Oh my god!!! That is kinda insane. That poor thing and its poor mother, I wonder what happened. Okay, so pedialyte and puppy replacement milk is great. At 4 weeks he'll only drink. In a week or two he will begin to taste solid foods, but all of his milestones may take longer without a mom to watch and follow. Wow. You can message me if you want my number so that we can text if you have any questions, that way I can answer quickly. You should check frequently to make sure he is warm; joeys cannot make body heat. This really depends on how old it really is. At 4 weeks I would say he still needs to be exposed to heat occasionally to warm up, but can retain the heat for awhile.
These are pictures of our joeys, who are 5 weeks old right now. I'm going to post them underneath the age as a heading so that you can match it up with yours as best you can. The younger the joey is the more work you'll have to do, because younger ones cannot stay warm alone. He should not FEEL warm, as their body temp is slightly below ours, but if he feels cool at all he needs to be warmed up. Being up against your skin is fine. Never sleep with a sugar glider because you could accidentally crush it in your sleep.
4 weeks old: