Wouldn't want many more than two nights in one, my back starts to feel it a bit.
I quite regularly spend a lot more than a couple of nights in a hammock. I also offset my pelvis a few years ago which leaves me prone to back pain, but I don't tend to suffer for spending a week in a hammock. I do however string my hammock tight, it's not sagging like a banana.
Whichever hammock and tarp combination you go for it's worth setting up so that the sides of the tarp are considerably lower than the bottom of the hammock with you in it. Set up so that you are side on to the prevailing winds, in this manner you'll cut out a lot of the convection current that can sap your body heat, it's still worth having insulation beneath you, be it a thermal mat or underblanket though.
On Hammocks, make sure you are happy with both the length and the tension that you can get into the sashes, if you are not then change them for others.
If you are camping when the weather is bad make sure you have something fitted that will stop capillary action of the sashes be it rings fitted or otherwise. If the water makes it along the sashes to the hammock it can be a very unpleasant night. If you don't have that fitted then take a bivvi bag to sleep in as well as your normal sleeping bag.
On Tarps. Decent pegs are a must.
I would also replace the guylines for the tarp with ones that have either a reflective or GID strip in them, this should limit the chances of you tripping over your own guy's and looking a burk.
Use small prussick loops to tension the top of your tarp to your ridgeline, a couple of mini carabiners come in handy for this as well. Crabs attached to the tarp and then prussicks attached to the ridgeline. Mini carabiners can be purchased from alpkit at a reasonable cost and I also got Y Beams (tent pegs, which I have been impressed with ) from them as well about 2.5 years ago.
My first hammock was a net one and I hated it with a passion. My second hammock was issued military hammock which worked very well as a human catapult until you got used to it. My third hammock was a "Thai Hammock" which was given to me by a Jungle warfare Instructor before I went away to do JWLRPC. I still use the same style of hammock today, an enclosable, which is the same as the DD Hammock and looks very similar to the TW Hammocks as well. I have now been using that style of hammock for just under 20 years.
Hope this helps
