1) i'm sure someone from your area will be along soon to let you know for sure on this.... but the only reason you would need 2 dishes would be if signal on the 129 is weak in that area and you need to pick up 61.5
2)they should be able to do it on one, but since you are prewiring the house anyway, i'd run 2 coax to each tv location. That way if you do add OTA later, or whatever, you don't have to worry about it. Its alot easier, cheaper, and cleaner to do it now than having to add it later.
3)see question2.... it can be diplexed in to the same coax as the satellite, but you are better off with a seperate run
4)Depends on the satellite or combination of satellites they use. If I HAD to guess, i'd say, no, you probably wont need it. They will probably use a Dish 1000.2 dish, which won't require the switch.
The switch allows you to connect 4 satellite locations to 4 different receivers.... there is a switch built into the 1000.2 lnb to connect up to 4 satellite locations to 3 receivers, which is what you will have. Even if you do need it, don't worry about it, they will install it when they install the dishes.