Since nobody has checked in yet I'll pipe in for what it's worth.
The saw you have chosen has been written up on this site as a winner. I've hardly any experience with Stihl, so I'm just going with what I've read.
Keeping in mind, that I'm just a guy who cuts firewood from time to time, I've had good luck with the Oregon Power Match bars. Any 20" bar you put on the saw would not be too heavy as to cause a balance problem. I've run Oregon Pro Lite bars on some of my smaller saws but for your saw, even though it costs a little more, I'd go with the Power Match if I were to purchase an Oregon bar.
Most of the chain I run is either Oregon or Bailys Woodland Pro. It is said that neither of these chains are as hard as a Stihl chain, so you may have to sharpen more often. Oregon and Woodland Pro are easy to sharpen.