I haven’t tried WAILA tbh, I like it in heavily modded MC with the stupid number of ores, blocks and machines that get added. Though for vanilla (or at least only with vanilla blocks) I don’t see the point but I can test it.
I managed to get JEI working but was struggling to get NEI to work. I disabled it for now but do want to get it working if only for the F7 lighting overlay.
As for the server, depends how you mean 2 different worlds. Yes we can have up to (i think) 8 worlds on the server. Though they don’t run simultaneously so you have to choose in your browser which world you want loaded.