MC Eternal creators recommend at least 5.5GB of RAM. However, that's the bare minimum and I'm not that optimistic that it'll run well with a few of your friends on it. Let's say you went with better RAM and got yourself a 6 or 8GB server, this will cost you around $24 to $32 per month on GameTeam. For the price, you get to play on the latest AMD Ryzen 9 processors and get all the side features for free including unlimited players, unlimited SSD storage, DDoS protection, and others.