Soo many questions...

Let's start simple, then go nuts, it really sounds like you're over-thinking it.

Like Catavarie said, skip the silnylon for a hammock... unless you like bathing in it.

General guidelines: 1.1 nylon <200 lbs, 1.7 - 250lbs or so. Double layered hammocks support heavier loads... has great prices, and the 1.1 ripstop (OD green) is awesome for a hammock. (I've made lots of stuff from this!)

Grab a 10' piece, hem it on the sides, add a large (3/4") rolled hem on each end and then gather it like Knotty's post says. Presto, you have a hammock!

Play with that, maybe add a footbox, or a bungee footbox, then make a bugsock... When the weather cools, grab more of that fabric and make a hammock sock..

If you want to go Cheap the no-sew Poncho Liner Underquilt is good to about 45-degrees, and is a 2-hour project that will cost about $30.

Happy Hanging!