Well I just finished. It was a easier than I expected. I couldn't use any spells except buffs since I had no mana income except the 2 you start with and later I had a staff that made 1/turn if I equipped it before hitting end turn.
I had the circlet that makes buffs on your champion free so I had stone skin and regen on him, but rank 1 of course since I had zero shrines.
I recruited 3 other heroes but one died while adventuring solo, which means he is permadead because I had no towns to send him to.
If they die in a group with someone who doesn't die then they just get injured and stay in the group.
My sovereign was a standard sword spec fighter, level 30 or so at the end with a 16 damage assassins blade plus a few other sword that had around 12 damage but +10 damage vs various creature types.
I had an archer and another sword fighter with me in the final quest battle (I did quest victory of course). Both sword guys died and my archer soloed the dragon. The archer did slightly more than the dragon was regenerating and the dragon cannot walk all the way to the back wall so it felt like a cheap kill. Hopefully they will fix that bug in the next version. I had the dragon down to about 10% health before my tanks died so it wasn't as bad as it sounds.
Several times I was in fights I had no business winning but I had a regen amulet (purchased from an opponent) and a horse and boots of speed so I would run around at 5 speed and heal 2 per turn until I could fight again. I beat several impossible fights this way.
My build:
40 attack, 53 defense, 49 init (would have been 51 if I wasn't encumbered)
Hardy, discipline, tarth, general, inefficient, wealthy, heroic, all the stuff that increases speed and hps and dodge and accuracy etc.
I had life magic 1 because I wanted regen, it was essential for kiting.
I used wealthy+traitor to hire some heroes and to buy horses and armor for my heroes from enemy shops. I had some very nice pieces of armor at the end from the computer because on insane they have really high research.
Towns:
I took over 2 opponent towns, one I sat in for 5 turns then razed because you can only raze 5 turns after you capture it. I realized I could never clear every town at that rate so I avoided them. I took one other that the computer took back before I could raze it. I tried not to anger the computer in general so as not to have to fight him at all. At the end I was at war with all 4 of the computers (small map 4 enemies) and their stacks were very tough fights that required careful play, killing archers first then kiting the melee while I regen.