How do you make a server Stable o.O? 
There's not really any good answers for that?
It depends on how you make it, almost bug free,
can hold up to 500+ players at a time without lagging
and crashing. Make one and find out? :)
Actually it depends how you handle the networking. And process all the bits and bytes, and say you created a networking that didn't use threads, I doubt it would be stable. Over-all it all depends on the networking.