Update - I started with a slightly earlier save, and it helped; they were just stuck on one shore... the dwarves couldn't get into the boats... but it was fun, really fun. I shouldn't have cleared out all the elves, I think I read about an agreement, but I didn't pay attention, or they'll appear anyway even if you don't clear out a particular faction.
In the third mission, it's tough with Bertrand. I gathered an army and got some good artifacts, but without darkness or summoning, it seems impossible, or maybe someone can show me how to defeat him without darkness or summoning?
I don't like playing with strong units through darkness... there, the mages aren't that critical, yes, but here I was leveling up a logistician, attack, defense, light, luck.
In the fourth mission, Dominic is tough, but I also went in with a more balanced or even smaller army. I finished him off when half my army was dead and I left him with 4 fanatics, but I wasn't upset, it was very interesting... although in reality, he would have crushed me. He's a bit slow, he resurrects, heals, I should have left 30 mana for antimagic and won, but I was in a hurry to finish him off, and I didn't have enough mana... and he was dealing 70 damage to me with fanatics... and where do the archangels get 40 mana from... I understand it would be a set of sar, iss, or light secrets, but not here, just too much mana, as if demons were pumping them up.
Update - I'm playing on veteran.