1. Perhaps I have misunderstood, but I can see this pretty clearly. It is right along the top of the screen. You can use <tt> in macros to heal the boss's target. Alternatively, I can press X to select the boss then up/down on the d-pad to throw a cure to a particular party member (maybe a DD who didn't get out of the red) and it will snap straight back to the boss.

2. I have not found this to be a problem, but you're further in the game than me.

3. You can resize and move every element in the UI, including this list in the HUD Customisation menu.

4. I haven't experienced this problem, but I play as a CNJ/WHM so don't have this ability.