The best you can do using the built in options is to try and toggle the HUD. You should see the red HUD button in the center of the top bar. Click through the options until you find one that suits you. One of the presets may suit what you are looking for.
For text sizing, there's nothing in game that I'm aware of. You'd have to manually edit the Lua files.
Another option if nUI's frames do everythng you need, is to install Clique. That addon will allow you to use a very similar click to cast feature as Healbot without taking up anymore screen real estate.
**Edit: You can also browse through the in game command line options by going here
http://www.nuiaddon.com/documentation.html