If using a mid cage GS derailleur with 50/34 front and 11/34 rear then a Roadlink will not be needed.
I'm using a GS derailleur with 50/34 front and 11/36 rear. It shifts fine without a Roadlink. I crosschain the crud out of it.
Any off the shelf chain will be long enough. The chain will need to be sized down to work properly. Start with the
Big/Big + 2 method.
-Tim-