I gotcha on the Whitehill fight - taking all 3 out would be a lot harder since you'd want to chain fight them like you were setting up to do and attempting to conserve Mana.
The only problem with Demon Portal level 2 is the randomness. When I tested it, I kept getting Imps / Scoffer Imps (I think once I got a Cerberus) and since the total Leadership of two Level 1's exceeded a single Level 2 then it was better to go with two casts @level 1; however, as you mention, if you can get a single Level 4 unit, then the fight will be easy - I just wasn't so lucky. Going with Chaos Level 1 will ensure that you have Meditation Level 2 at Daert Level 5 (4 if you're lucky) for 2 Demon Portal level 1 casts.
I would not pick higher than Level 1 Chaos until you defeat the Dwarven Shelter stack so that you can either pick Meditation Level 2 or Chaos Level 2 as the situation is warranted for the Elven and Human stacks. Give yourself some flexibility so that if you are lucky and can get a Level 4 Demon troop then go that route. If you can't then go with more Mana.
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