What do you need to have and know to create a campaign for Heroes 5?

Inner Strength 2? :) As far as I know, you can create a campaign in the second expansion pack. I'll be waiting for the campaign to be released.

You can also do it in the original version with patch 1.5. I'm attaching a screenshot showing where to click to combine missions into a campaign.
P.S.: There are already Russian campaigns available - Day of Fiery Tears by Ogo.