Hello and welcome to HF!
As NWOHanger said, the rings are for the double bubble pad (but could also be utilized with other pads as well - but you'd have to fabricate your own attachments on the pad). The velcro on the outside is for holding the bugnet open. Look along the zipper close to the bugnet about halfway down and you'll find the matching velcro patch to mate with the one on the non-zipper side.
"Improvements" are really an individual thing. Get some time to use it as is for a bit and then you'll have a good idea of what works well for you and what doesn't, and what could use improving to make it more useable for you. Personally the stock setup works well for me and there isn't much I would change as it is a well designed package IMO. That said, some of the often recommended changes:
1. Bigger Tarp: The stock diamond tarp is considered small by some, and a bigger tarp is really nice for the extra living space it provides in bad weather. The Hennessy Hex tarp is a good upgrade (if you didn't get it already), and a multitude of tarps are available from many cottage vendors that have great quality and service. It's also nice to use a seperate line to hang the tarp from as it provides a tighter/more adjustable pitch than using the hammock suspension prussics.
2. Suspension: The Hennessy lash isn't easily adjustable. Whoopie slings, cinch buckles and the Garda hitch (using rappel rings) are some of the more popular options to switch to for ease of use. Personally I use a Midshipmans hitch (a tautline knot) that provides adjustability without additional cost or hardware.
3. Tree straps: The 42" tree straps that come standard can be too small to reach around larger trees. Hennessy offers longer ones, or you can make your own from polyester webbing salvaged from ratcheting tie down straps.
4. Snakeskins: If you didn't order them with your hammock. Fantastic method for quickly storing/deploying either the tarp or the tarp and hammock. Either the Hennessy version, DIY (do-it-yourself) or again several vendors offer different versions of these.
If you haven't already, check out the videos stickied at the top of the Hennessy forums - some good info and ideas there, as well as reading past posts from all of the areas here at HF. Lots of great info is at your fingertips.
Hope that helps!