Lovelyrosepedal is correct. Different species have different antibodies and some diseases can show no signs if carried by that species, but if placed with another in which that species does not have the antibodies to fight off those diseases can be deadly. Another thing to consider is bullying. Especially with sulcatas. I have 10 that I held back from 118 I hatched out this year. Each clutch hatches about a month apart. The 3 month olds wont bully per say but are much larger and eat up the food and have the upper hand at getting to the food first. This is why they are kept seperate. If these were kept together the smaller younger ones would become stressed and begin to spiral downhill, and could even die if corrective measures are not taken into account and revisions were to be put in place. The other factor is the size in futuristic planning. These guys will get huge very quickly. The more you have the more room you will need. Especially in the case of them possibly all being males and becoming sexually mature and could become very dominate and fight. Leading to similar issues with the young ones just being 1 month apart, You would need to seperate them, and that can become a challenge if you do not have the room. I would suggest a different species in a totally new enclosure, and or if you have the room and means and methods to seperate or keep them housed in a very large enclosure to where they can seek refuge and not stress one another by all means, get some more. They are creatures of habit, and still very very wild even though domestically produced. They dont really want or need "friends". Just pointing out a few things to consider before adding more. If your prepared and see things through to the future and want to take the neccesary measures in good planning and possibilities of maybe having to adjust the enclosure and living situations then go for it. Just make sure your decision is rational, and is best for the animal(s). Good luck, Its hard for me to go to reptile shows. I always add more to the group,(usually ends up me having to make another habitat. 
