Uhm you need to upgrade majorly. With 1gb of ram you'd be lucky to have one gameserver run let alone all 4-5 to avoid lag. And 1gbps? Just to clear it up, you don't perhaps mean processor speed of 1ghz or maybe 1.0Mbps for your upload speed? What is really important is RAM and upload speed, not download.
With 1.0Mbps upload I "think" it will manage 20-30 people, maybe max 50, i'm not really sure and it may lag before even reaching those numbers. Never tested myself so don't take my word on it. With 4gb of RAM you'd be able to open all the main maps, argent, icicle and shaitan. Of course if it is all at a home pc and your upload is really that slow I suggest opening them all on different gameservers so that it doesn't lag.
Depending on what you want to do and what you want to open, you will need to upgrade. I personally opened a server just for testing on a pc with 2gb ram with all 3 main maps ONLY and only me and a few other ppl, not even reaching 5, were on it. It put a bit of a strain on my pc after awhile, and considering it was an older pc it was expected. Still for the best performance go for 4gb ram and atleast 2.0+ Mbps upload to handle the gameserver memory useage and atleast 40+ people being on without lag. Of course there are alternatives such as using mini versions of the big maps or a single big map as the main map for all. Good luck on w/e you are trying to accomplish though.
