WELCOME ABOARD!
As for what mods are the best, every one of the thousands of players will tell you something different. There are four different supermods, all good and all popular, and dozens if not hundreds of mods that work with some or all of them.
That said, GWX is the most popular, and most agree the most rounded of the lot, giving a good balance of graphics, sounds and gameplay. If you make that your choice, your next stop should be this thread:
http://www.subsim.com/radioroom/showthread.php?t=170090