One satellite (101) is used for national and local SD. 110 is used for national HD, 119 is national HD plus some local SD and LA/NYC HD locals. The two new satellites at 99 and 103 are use for local HD and regional sports network HD. Two addtional satellites at those locations will be launched next year providing additional local and national HD channels.
Up to four cables are required from the dish. These will feed four tuners (1 per standard receiver, 2 per DVR). If you need more, the four cables need to be run to a multiswitch with 8, 12 or 16 outputs, depending on model. If you only have one DVR, two cables will be needed. In any case, for OTA digital locals you will need an additional cable.
The OTA input on the HR20 is disabled, but is expected to be activated very soon (the software apparently wasn't ready). Hopefully dual buffers will be activated as well in a software update.