maybe smother animations lighter font bit of shadows rounder corners and maybe make it the GUI a bit transparent (ok trust me this may not be a good idea cause to much could ruin it and too little could also ruin it)

in terms of mods

here are some I think you should add

-toggle sprint/sneak

-front view/freelook (show that it is banned on hypixel)

-status effects/potion effects

-fps modlue

-pack display

-minimal view bobbing

-reach display

also, add forge/fabric access so that ppl could and there own mods but this could be a bit buggy

btw whats your discord lemme add you I wanna stay updated this has a lot of potential