This is great - I really appreciate the feedback.
I thought about burying an additional ground rod because of the drawing here -
http://www.hdtvprimer.com/ANTENNAS/basics.html - that shows a ground rod plus an NEC-required #6 copper run. Service to the house is grounded to the water pipe from the street that emerges in the basement, before the water meter. Tying into that should be straightforward. However, this is roughly 30' from where the ground wire might enter the basement. Using #10 solid Cu wire as in your post #20 would be a considerable savings over the #6 wire suggested in the earlier link. I wonder if the #10 is up to a proper lightning discharge. Looking at lightning rod wire, it's a #1 open braid at about $2 per linear foot.
The roof peak is about 24' off the deck, and there is a location around the corner from the picture that would support a 30 foot-ish mast from eves at about 12 and 20 feet (picture will have to wait for daylight). But I'm unsure about how a mast like that would be erected - ie whether the antenna(s) would be assembled to the mast, or if the antennas would be assembled to the mast after it was erected.
You mention roof brackets - the roof you see in the foreground of the picture isn't that high - maybe 12'. So that's another 12' to reach the roof peak. The location around the corner seems more practical, if using brackets. Then run the mast to the ground. Steel tube is cheap compared to heavy copper wire.