Quilts for gathered end hammocks are essentially interchangeable. Hennessys are different with their asym lay, and any other hammock that has tie-outs to increase roominess will have those tie-outs get in the way of a regular underquilt.

The UQ suspension attaches to the hammock end of your suspension- most come with s-biners or an easy way to clip into the continuous loops at the gathered ends, but it can be acheived with knots if you have no hardware.

So, while your tarp will have its own suspension, the underquilt shares the hammock's suspension.

Speaking of the tarp suspension; are you going with two ridgeline tie outs on either end or a continuous ridgleline? If a CRL, above or below the tarp? I've been using two individual 12' tie outs with Dutch wasps on either end, but am considering switching to a 30' CRL so i can use snake skins to stargaze until the sneaky storm starts sprinkling.

The Superfly is a great tarp. I really have been liking the silpoly tarp I have currently, but it might be a DIY-only option as I don't know if any manufacturers are making silpoly tarps.

Definitely check out hammockforums, where they've hashed out the nitty gritty details many a time.

The fiddle factor is high with hammocks. Almost as high as the comfort factor.