You can not change the level of transparency, the skin will never be 100% transparent.
Every screen has a back button that should take you to the previous screen, which most of the time IS the main menu. Which screen do you want to add this button to? There are very few screens that are multi levels deep.
as for the weather. Yeah, ive thought about it a few times. I actually have the code for it too for a long time. Its just been pretty low on the priority list. I try to stay away from the weather screens as there are a ton of labels. Ill try to move it up the list.