I think that a second sugar glider might help my little boy in many ways. Keep him company, playmate, a friend, the list goes on, but I have a few questions about getting a second one.

Many people say it's best to get one that's the same size as the current one. Will it still be okay if I get one that's younger and smaller in size? I'm aware that it's not the best because it gives one a better fighting advantage over the other, but I'm just curious.

I want to get a female for my baby boy, would a second boy be better or will it be fine if I get a girl? I'm planning on getting him neutered soon, or at least consulting with a vet about it (if I get a female).

-OFF TOPIC Q- Do sugar glider females ever go into a state of heat, like unfixed female cats?

I got my first suggie from a pet store, I know that in the U.S. it's not a smart move and you should get them from breeders, however, I'm not sure about Malaysia since they're sold in just about every pet shop, but should I find a breeder instead?

Just so that it's not repeated in your guys' replies, I know the following:
-Both must have a checkup with a vet for any diseases/bacteria/other.
-Keep them both in separate cages for a few days to adjust, and slowly introduce them to each other.
-Same size Suggies are better.

If you do get a suggie in a smaller size, don't introduce them until shes big. I believe females do go in heat, cause every now and then my female gets really irritated with my male lol. As long as your boy is neutered before they meet, a girl is fine.

both should be in a separate cage for as LONG as it take for you to feel safe they can be introduced without fighting. A few days sounds short, we did scent swapping for 1 to 2 weeks and cage close together for at least 7 days. Even then I thought we rushed things alittle. BUT all our introductions went very well and very easy over all. seems like gliders like having company. our gliders ranged in different sizes, and that didnt seem to hurt anything, for introductions. in fact our colony of 7 has one malcontent, a very skinny female, she runs around giving chase to some of the others part of the night, we are trying to get her bonded to us, if that doesn't fix her aggressiveness she will have to be moved.
I don't think boy or girl second glider matters, just get male neutered.
Our females seem to go into heat, they want less to do with us and the males get all over them.

Females do go into heat. The only way I can tell when she is in heat is by the way my male bothers her.

Great, thanks everyone for all the help!