Okay so I just recently got a sugar glider so I'm semi-new to this.

For the first few days he barked a lot at night and I knew it was because he's nervous about the new place and all. But just today he started to not sleep unless he is in his pouch with my hand in there with him to cradle him. Every time I remove my hand he wakes up and stares at me until I put it back.

Is this a problem? Should I be worried for his sleeping habits later on?

I'm a night-owl and like to stay up late, so I'm usually up late at night and keep him out with me. But during the day I'm at school and don't get him until 4pm. I'm worried that he won't sleep while I'm not here since he wants me to hold him every-time.

What should I do?

I'd consider a cagemate but also research quarenteeming them before they physically meet. Vet check new arival with stool test to be sure there's no contaminants it may spread to your first glider.
You may not need a cage mate but as gliders are very social colony animals they do better in small groups generally.
The barking can be very normal and mine bark every night but I reinforced it by always giving them treats and attention.
Also a good idea to get a digital scale to weigh him in to monitor weight. If they lose weight due to stress or loss of appitite a drop it there weight could be a warning sign that he's lonely or unwell.

Overgrooming is also a sign of loneliness, but remember every symptom can mean multiple different things so vet checks are the best option if he is showing signs of illness.
I can't believe you JUST got him and he already wants to be with you all the time! That's honestly amazing. I've read a lot of posts here about gliders always wanting to be with their human and not sleeping without them, and my boy is honestly getting at that point too -- he's a single glider.
I feel like if you take him out and play with him in the early morning or late at night (around feeding time) and tire him out, he'll probably sleep without you around.
When I remove my hand Tveit stares at me and won't sleep until I pet him again too. If you don't want to pet him any longer then just give him some time to realize you're done and see if he goes back to sleep.
Make sure there is natural light during the daytime wherever he's sleeping, and darkness when he's awake.
If you're really worried about whether or not he's sleeping while you're at school, you could get a mini camera and set it up to watch his cage during the day and see if he's asleep or constantly awake.
Some gliders just can't handle being alone, which is normal for them since they're colony animals. My boy has never been with another glider, and I feel that's why he doesn't have the ability to "miss" having another friend.
If he's barking a lot at night, he may need more stimulation. Try putting a lot more toys in his cage to keep him occupied, and switch it up for him every so often so he's always "discovering" new things. They are very smart creatures and need a lot of stimulation.