1) I'm pretty sure that you can program the AUX button on the Dish remote to control a second address; never tried it myself, but that's what I'd read about in the manuals.
2) Rain fade in the Western Arc happens very rarely. You're in Columbus, so you could wind up with Western or Eastern Arc service. The weather has to be BAD for a properly-installed 1000.2 dish to fade out. If you don't mind spending money, there are ways to further discourage it, too, by buying your own dishes and a multiswitch.
3) You can also tell your timer to record to external automatically, can't you?
4) Full HDTV (MPEG2) is 19Mbit/sec; typical Dish HD bitrates (MPEG4) are less than half that. USB 2.0 is 480Mbit/sec, so it can theoretically support...25 concurrent HD I/O streams.
5) A pair of 621s will fit your needs nicely, but a 722 and a 621 or a pair of 722s would give you a LOT more flexibility.