What is the recommended number of slots for 4 GB RAM? and 6 GB RAM? I have the unlimited plan with 6 GB RAM but I'm thinking degrade my service to 4 GB RAM
It really depends on your usage. If your players are all in the same area/chunks, you won't need as much ram to handle more players. If they're spread out, more ram would be needed. You can check your ram usage right now, and if you're not using what you have, downgrading wouldn't really affect your server(keep in mind there are also storage limits for the non-unlimited plans). You'll only need more ram if you're crashing from out of memory errors. What's shown on your Multicraft panel or in game isn't that actual ram usage, since just because it's 'using' x amount of ram doesn't mean it's being fully utilized. You should try setting your slots at a lower amount, then as your playerbase grows, raise it as needed. Sometimes too many empty slots can drive players away from joining.