Price is rather good. The standard units dont come with HDMI only the black elite units have them.
20g if all your doing is game saves is plenty should be no issues there at all.
the newer white Pro bundles (generation 2 and above) have HDMI's as well, at least mine does.
It depends on which generation of Xbox360 it is if you will get a HDMI port or not, I am going to assume launch generations because they had the biggest problems (Heatsink and Mobo clamp issues leading to three wonderful red lights) and those don't have one. But you don't see much a difference between 1080p and 720p on a 360 anyway (I don't). If you wanting to use the 20g just for saves, then go with that because you will still have a good amount of room on your drive for must have XBL arcade games (Castle Crashers, Braid, etc.). Overall a good deal I believe.