The Nook uses the Adobe mobile reader software. Therefore it has the same quirks as any other Adobe based reader.
Basically if it works in Adobe Digital Editions (on your PC), it should work on the Nook.
The nook supports the at least some float ability, as that is how one does drop caps.
I don't know about borders and background colours, you will need to test it out.
It supports embedded fonts (fonts included in the epub and referenced in CSS).
I have no idea what Media Queries are...