What is Bacco?
Full champion, so he splits experience.
do henchmen also XP split with other heroes? With other henchmen?
No and no.
Should it say somewhere in Bacco's unit details that he is a henchmen/hero?
Henchmen don't get unique background text, while champions do. Plus, henchmen typically have names like "Torchbearer" or "Bard," rather than names which are proper nouns. While it might be useful to have something somewhere indicating that a unit is a henchman rather than a champion, it's relatively easy to see the difference if you know the above.
Other differences are that Henchmen don't have access to full magic schools unless you use one of the spellbooks on them and instead may have access to the Air/Earth/Fire/Life/Water Adept trait lines, and they have a few unique traits available (Cook, Shieldwall, Bard, maybe something I forgot), and are all of the race of Men unless created via XML edits.
The only thing I haven't tried yet is randomizing the choice of champions that choose to face you in combat. Certainly you chould 'choose' which Champion ends up facing you via a quest choice option, but the Dialogue/position in the dialogue options would give away which Champion you'd be facing. So while you might have 5 Champion choices, well they'd be the same 5 Champion choices, so again, although having multiple choices besides Bacco, it'd still get repetitive after a while...
You could do it in a way similar to how they did the Rats in the Ruins quest, and make multiple copies of the quest and include your differing champions there. If you wanted them to be mutually exclusive, you could perhaps include a new hidden resource that you have one or two of when you start the game and have the quest take away from that resource, if that's a requirement that can be tacked on to quests.
