I've been going for 200% completion for 2 days now, 12 hours each.
So I assume a full walkthrough of the map once will take another 5 days at 12 hours each.
It's unlikely you'll be able to handle going through the map a second time here.

By the way, as can be seen, diplomacy is not forbidden.

And is buying heroes with a 4th level spell specialty not forbidden?
Can the Cloak of the Undead King be used?
Can spells like Fly, Dimension Door, and Mountain Portal (if they happen to give them) be used?

And one more question. The phrase "digging up artifacts" is often used here.
Digging up the Grail, I understand.
"Digging up a hero in the tavern," I also understand, meaning searching for the right hero.
But what does digging up artifacts mean? Does it mean that in the merchant, for example,
on the 1st day of the month different artifacts can appear, yes?