You have to have the original game files either from the disk or downloaded from GoG or steam. Then you need tes3mp which runs great on linux and windows. I personally play on a server called neravarine prophecies, they have seasonal events and the community is a lot of fun. It uses the same engine as openMW so most of the mods that work on OpenMW are compatible, I'd stick with cosmetics to keep the servers you join compatible.

Different servers have different rules, many of them forbid going into areas that cause server crashes, i.e. mornhould.

I had a blast, then I got my kids to play and i was there to guide them a bit when the game gets tough.