Hi Guys.

At the most basic, what needs to be set to trunk between two CRS using SFP?

Bump. Nothing special that needs to be added using a single connection?

Exactly nothing. You just connect two switches together using some network link (via SFP in this case) as long as the SFP port is enabled and in a switch group with all other ports - this is the default configuration.
You only need changing the routers default IP addresses (192.168.88.1 by default), so they can be accessed to your liking, which is kind of obvious...

http://wiki.mikrotik.com/wiki/Manual:CRS_examples

That should get you started in the right direction.