Looks great!
Re background -- i like something with a little less color/lines to help the buttons/content stand out against it..
re text size/weight -- css changes should work, as long as you are targeting correctly, and they aren't being over-written by other css code. you should be able to use the dashboard settings dialogue, to up the text size and spacing for the tiles. this might help a little bit. Im not sure exactly what you are trying to modify with css, additional details may be helpful to get you a good solution.
I really like the qr functionality for guest wifi. can you explain how you did this?
for bypassing open contact sensors, you may want to take a look at:
