I'm not sure if one fabric for the hammock would be better than another. It should still be covered by a tarp and/or the overcover precipitation protection. Ultimately, you should go with what you find most comfy (ripstop, taffeta, etc.) as that'll be most important.
If it were me, I'd go with that 1.8oz Night Grid Camo taffeta. Looks great and should be very comfortable. In the end, though, all are probably good - I've slept on tafetta and several different ripstop nylons and never thought "boy, I don't like this one".
In terms of 60 vs 72... the 72 would definitely give more room but might end up flapping with all that fabric. Also, the length is considered more important than width in comfort. At your height, I'd go with the 11-foot model and probably split the difference in width and ask for 66".
Underquilts are definitely worth it, if you can afford them. They're widely considered to be the most comfortable (nothing impeding with the hammock) insulation option and are generally warmer than pads if you get one rated to what you need it at (they also avoid condensation issues, etc). Some of those issues become even more important when it gets really cold - I wouldn't want to fight with a pad at 5 or 10 degrees. At worst, you could get a 0 degree UQ and then supplement with a pad if you plan on going really cold.
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