I do use a pad when sleeping in my hammock for additional comfort and warmth. I am currently using a Big Agnes sleeping bag with the Big Agnes insulated air core sleeping pad. The big agnes bag has a sleeve pocket on the bottom of the bag to slide the pad into so it stays in place when you sleep. This combo works very well with the hammock in my experience.
The rain fly I use is the one that comes with the hammock I linked to in one of my earlier replies. It is 76 inches wide and 115 inches long. I have used the setup in multiple rain and snow storms and never got wet.
One drawback with the hammock set up is it is tougher to get dressed and ready in the mornings when it is cold but I have gotten used to getting dressed lying down in my hammock, so not a huge deal.