You no longer need a SuperDish for locals, recently most SuperDish locals switched to a new E*spotbeam satellite at the 110 location and only need a Dish500 now for locals, unless your locals are Charleston-Huntington WV and a couple of other market exceptions which require a Dish1000 for the 129 satellite location.
Yes you can do this, many here do, I have in the past. You could also home run the wiring of some or all of the 4 tuners to a distribution panel, set one tuner to channel 3, one to channel 4, the other two secondary tuners can be set to unused UHF channels, this will give you more flexibility because you can then watch any 4 tuners on any of your 6 TV's, channel 3 and 4 can only be used if you are not getting them ota however and you may also need a channel 3 or 4 signal combiner to prevent bleadover of adjoining ota channels. The preferred way to connect your receivers to your 2 primary TV's is through A/V and S-Video for better picture and stereo sound.
I would also suggest getting at least 1 625 DVR, until you have had a DVR in your home you do not know what you are missing, these things will change the way you watch TV for ever, best thing since sliced bread
. Now that I have a DVR, I would rather give up a few channels and go with a smaller programing package then go with out a DVR.