With ~2GB RAM I was able to have full geodata (no pathnodes) and more than 70 players without lagging. Although as Copyleft said, the EQ4 is a more suitable server.
I used the exact x3 server few months ago and i had 500 players and no lag. I just used geodata where it was needed (castles/popular zones), no quests etc. But thats ok if you use it for high rate as i did, but if you want to make a mid-low rate with everything rent a x4 and above.
P.S: If your looking for a server that can handle over 1k then go for the 8gb ram ones.
What i would like to ask is how to increase the maximum memory which the server uses, I have tried by increasing the Xms but if i increase it for some reason the server doesn't want to start up :/
Then probably you are trying to assign more memory then is allowed for a 32-bit process. I believe the limit is around 2G, but with java and it's JVM it's probably even less.