With the highest respect. I feel like this is likely a problem on your end, perhaps an older laptop, or maybe dusty. But there isn’t anything special about UII that I can think of that would cause a laptop to get hot, other than usage. The main menu is a level in Unreal Engine, so perhaps that’s why it takes a bit of resources.
I don’t receive any input lag. Do you experience input lag while playing singleplayer?
All UI is in a placeholder state as far as I know. The UI he has looks like untouched UMG Widget Blueprints, I would be shocked if the UI stayed in its current state permanently.
Take a look at a post I made a while back talking about documentation.
In short Molt says documentation is a huge priority in UII, you can see the beginning of that here on the wiki