I really like that the game has a built-in means of adjusting the UI to whatever you like but it's very hard to use it effectively. I suggest three changes that would make it much easier to use.

1) A snap feature for hotbars. Players often stack their hotbars either side by side or on top of each other. Ensuring they are lined up would be easier if like items could snap to each other.

2) Coordinates of the selected UI element shown on the screen. Trying to line up my hotbars only to find out they are one or two pixels off from the others is beyond infuriating, especially when I have to use the mouse to try and be precise.

3) Using the keyboard to make minute movements on the selected UI element. Using a mouse isn't nearly as precise as a key would be. I envision the ability to use the arrow keys to move a UI element in all direction in a precise unit of measurement, like 5 pixels per key selection. Combined #2 this would make redoing the UI a lot easier.