Any question answered...

I'm hoping to be proven wrong but wouldn't there be too much cable travel with the new Dynasys actuation ratio for a bar end shifter?

I was thinking of a downtube lever, they usually have a bit more spare capacity.

Wouldn't the derailleur be too narrow with the 8 speed chains?

If it is, you can shim it, but in practice the cages aren't usually so tight that the extra 1.3mm is a deal breaker.