Well there is always the chance that the people makin SG will bring in the race again. Hell, they could have the Prometheus get destroyed and send the whole mod to hell. But we just have to make it with what we have right now and just hope that they dont change anything too much.
They seem to have technology close to the Asgard. They have remote teleportation as well as auto tracking energy weapons aboard their ships (either that or gunners that are realllllly good). But whatever the case, I'd say they're neutral. The Goa'Uld may have infringed on their territory and pulled out because they were too powerful. They certainly dont have any interest in making friends, considering they fired upon the Prometheus without being attacked first, even when they were hailed peacefully. We know they understood because when Carter hailed them and made the little deal to get out of the gas cloud. We also know that they aren't a race hell-bent on killing everything in sight, because they actually complied with the deal and didnt blast Prometheus as soon as they got out.
My guess is that they dont really care for other races. They probably abducted the crew for scientific study or something like that.
The availability for expansion is pretty large, actually. We could say that while Carter was alone, the Prometheus picked up distress signals from the craft whch were later discovered and decoded, allowing for better communication. They could have been saying something like, "this is (race name) vessel (vessel's name/ID/whatever) ..." Maybe one of our smaller ships (the one's we're making up for this mod) goes to their systems broadcasting a peaceful signal and making friends. Maybe they are like the Tollan, who will be friends but aren't gonna share anything with us. It all depends on what we feel like making them.
As for the Aschen, I say we hold out until that episode Black Wolf was talking about comes out. It's the safest path, plus it would have great source material.