Welcome Fitz. I'd check out this site for a great intro into keeping warm in a hammock, as well as lots of other hammock stuff.
Also, check out Shug's intro videos that he recently did. Learn & have fun at the same time
On the single ridgeline for hammock & tarp, that's how the Hennesey hammocks come stock, but I believe most people end up using a separate guy line for the tarp because the tarp sags when you get into the hammock, even if you had it nice & tight before getting in.