I started out on a DD hammock. I can add this:
- indeed, the distance is not (very) important, as long as yuo get the right "tension". You develop a feel for it after a while, even if you don't have the ridgeline. I used the DD with its webbing suspension, so I had to have that "feel" pretty quickly, since re-adjusting was a bit of a chore.. This will also deal with the ridgeline need - get a feel for how to hang, and you won't need the line. I also used snakeskins, and found it easy after a while to gauge the tension while the hammock was in the skins. Once you've tied it up to the trees, take a couple of steps back and look at how the boa constrictor hangs between the trees.
- the DD hammock benefits IMHO of hanging somewhat tighter than e.g. my wbbb. The 30 degrees is a benchmark, but I usually had it way tighter than that. Your hang may vary.
- the not level hang is preferred by some, keeping your head lower. I always strived for a level hang, and that is another thing you'll get a "feel" for.
- the tarp thing sounds a bit weird. Anyway it should be resolved once you start hanging with trees further apart! I use the same tarp, and I like it because I can hang it a lot higher and have coverage and headroom at the same time. I hang it independently from the hammock, meaning I don't take the hammock suspension position into regard. I also used a line underneath the tarp, which I attached the bugnet cords to.