30i is thirty full frames per second sent as 60 half frames (similar to NTSC TV). 30p is thirty full frames per second sent as 30 full frames.
Not quite - HD
1080/24p, 1080/30p, 1080/30i (x1920, Square or 16:9)
720/24p, 720/30p, 720/60p (x1280, Square or 16:9)
"Enhanced Definition" is...