There was a discussion on the board some time ago about old thread deteriorating. I can't remember the explanation, but since then, I've tried using up my older thread first.
I like the idea of using cotton thread with cotton fabric, so I've only used Superior Threads King Tut on my Sweet 16, top and bottom, and am happy with the results.
I don't think you can go wrong with any of the fabric sold at your LQS, which are the same brands sold by on-line vendors. I love the texture of Art Gallery fabric. I only buy yardage and FQs, so can't recommend a vendor for accurate jellyrolls (I've heard they are not always cut consistently).
Fabric Shack is one of my favorite on-line stores. They have a good selection, it's easy to search, their service is quick and the shipping price is very low. For modern fabrics, Hawthorne Threads is great. I also frequently shop at Shabby Fabrics and Fat Quarter Shop.
Welcome to the board and to the wonderful world of quilting!