I also have the Explorer Deluxe...you'll enjoy it!
The stock tarp is ok...you'll probably choose to upgrade it at some point, depending on your camping habits.
For under insulation...for right now, you can get away with just using a pad inside your hammock, under your sleeping bag. Inexpensive, and it works ok for most folks. You could buy two of the blue wally-world pads and cut them up and put them together to ensure that you have sufficient width in the sholders and so they stay in place better. MUCH cheaper than HHSS or UQ's...but more bulky and a bit less comfy. Good interim solution.