What if any supplements do they need? They should have a diet that is approved by one of the sugar glider owners on this forum. Check out the BML and HPW diets and see which one fits to you. I am sure someone will post links to these.
Should I have something on the bottom of their cage? I use Puppy Pads, you want to avoid Cedar chips as they are toxic to a glider. Newspaper works but if they get a hold of it thru the bottom of the cage they could eat it and it has ink in it so that would be bad. You will definitely want something on the bottom of the cage though.
Would a baby/young or older suggie be better for a first time owner? If I did end up getting one I was going to start out with one and then get a friend for him/her is that ok or should I just get both right away? This is my opinion but... I would get two baby gliders or young ones that have been handled a lot since being OOP. It is my opinion that you should just start out with two since they will provide comfort to each other should you not be able to spend as much time with them as needed. If you only get 1 glider it could become very grumpy and lonely.
Where is a safe place to play and love on a suggie? Get a small 2 man tent and set it up and take some treats into it. Or go into a small room and "glider proof" it. Make sure they cannot escape or climp under anything or eat anything that may hurt them. The bathroom works well for this, just make sure to seal off the toilet.
Are leashes safe? My OPINION is no, they could tear the membrane that the gliders use to glide with. Some people use them but I wouldnt.
Do suggies need a bath and can you give them one if the need it? As far as I know, you do not need to bathe them. They dislike water on them for the most part. They do a lot of self cleaning while in the pouch from what I have seen from my two.
What temp should the room that the suggies are in be? they say the room should be from 70-90 degrees Fahrenheit. I personally cover the cage with a blanket on colder days just to make sure they stay warm.
Just FYI... all of your answers are already posted on this board, you would just need to do some searching for them. Some of the posters on the board here get irritated at people when they ask the same questions that have already been posted. Use the search feature and you will find a ton of info.
Have a good one!
Frank