The FCC says you can install an antenna on your roof:
http://www.fcc.gov/guides/over-air-r...n-devices-rule
You will have far greater chance of success if you mount outdoors. If you are mounting in the attic, you'll have better success if you can aim through the gable end rather than the roof deck and shingles. Some attics are very poor antenna locations, none are great. You're already at marginal signal levels and the terrain you've described may add to the challenge.
I have no reason to dispute the sellers comparison testing but the HD Stacker is difficult to recommend because there is no published data regarding gain and beam-width. I'm left with only anecdotal information to estimate how the antenna may perform.
A Winegard HD7084 would offer FM reception that the HD stacker lacks.
I doubt you will receive real channel 2, 5 or 6 reliably, those frequencies are subject to more noise than channel 7 and higher. And, your TVFR indicates they are going to be weak.
Unless you plan to use the cables for a satellite system in the future, quad shield cable won't hurt, but it won't help either. If there is any price difference, go with the lower cost of double shield vs. quad.