The first thing to determine is how many inputs and outputs you need (4 inputs for 2 or 3 LNB dish - 5 allows OTA signal to be added). One output per satellite receiver is needed except in the case of D*TIVO box which uses 2 outputs.
Mechanical multiswitches will be less expensive while electronic switches will be more costly. You can search for "multiswitch" for complete details.
Nope. Sat C combines with Sat B through use of a special LNB and combiner before it gets to the multiswitch (although some multiswitches have the Sat C combiner built-in) Search "Sat-C kit" for more.
Since you're in the HD Hardware forum, we're assuming you already have an oval dish or are about to get one. If your oval dish already has an integrated multiswitch, then the four outputs can be run directly to four receivers. If not, then you're looking for a 4 or 5-by X (the fifth input port diplexes over-the-air signals from a standard antenna) "X" equals the number of outputs you'd like.
If you have a dish with an integrated multiswitch and you need more than four outputs, search this forum for "cascading multswitch" to find threads on how to do that.
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