Risk of Rain 2 server hosting: short runs, lots of entities
Risk of Rain 2 works differently from the survival games on this list. There is no persistent world: you play runs lasting half an hour to a few hours, and then everything starts over. That makes the server load quite different too.
Entity count is the bottleneck
The further into a run you get, the more enemies, projectiles and effects are active at once. In the late stages of a long run that can reach hundreds of objects all needing calculation. That is where your load sits — not in player count, which is capped between four and sixteen.
A run that felt smooth on stage 3 can stutter on stage 12. That is the game, not your hosting.
Why a dedicated server helps
By default one player hosts the session. If they drop, the run ends for everyone. With a dedicated server the lobby stays up and you can simply start again without depending on one person.
Mods with BepInEx
The modding scene runs on BepInEx and R2API, usually managed through Thunderstore. As with most games, server and players need the same mods.
How much RAM
2 GB is plenty for a standard lobby. If you run heavy modpacks with extra survivors and items, 4 GB is sensible.