It looks like you are going in the right direction to me. You may have an issue with a switch trying to be a principle switch and pushing all of its zoning data to the other switch. You may want to add the zoning data from the switch with the higher domain ID to the switch that will become the principal switch in the fabric.

Everything looks fine here and you should have no problems with the merging of the zonesets. You have already made sure that there are no duplicate zone names, so there is no problem.

You don't need to worry about the zoneset names. They won't affect the merge.

The only thing you may want to add to your list is verifying that the ports you will use for ISL are enabled and configured to allow E_port connectivity. You should also verify that the ports are not artificially limited to 1GB or something.

When you chose the ports to use, did you pick ports from seperate cards? If not, you should consider it as it will allow you to survive a card replacement without fragmenting the fabric.