Congrats, hope you really like it. I have two Explorer UL models and I still rate them highly after 6 years of hanging with several different highly regarded hammocks. Sure, there are other hammocks that are also way excellent, my I have been happy with my Explorer ULs.
As for insulation, there are any number of excellent UQs you can pick from. I wouldn't know how to tell you to pick one over another. I use JRBs, a brand which was originally designed especially for the HH models, and they work perfectly. With a zip model, my WB Yeti works great also with a foot pad, and saves some weight. There are several other highly rated vendors, I'm sure any of them would be just great. Some how, you will just have to pick one!
Since you have the small stock tarp, with it's weight, bulk and only 2 stake advantages, I will throw out another alternative for you, the controversial HH Super Shelter. start with this thread and then check other threads to read up on it:
The reason I am suggesting that is that, even with the small tarp, you should have no worries about staying dry in bad storms, or worries trying to keep a down UQ safe from sideways rain with that small tarp. Reason being that the HHSS Undercover provides waterproof protection in addition to any tarp you might use. But if you think you might go that route, I suggest you read up on them here at HF. They are not for every body, though they work great for quite a few.
And if some extra bulk is not a deal breaker, don't forget the synthetic UQs offered by Paul at AHE. ( Jarbridge etc ) Both the HHSS and these synthetic quilts will also save you a few bucks. But they won't pack down as small as 800 FP down, though the HHSS open cell foam pad actually compresses down pretty well.