kennec, I am level 17 as well so we are at the same stage. I am currently clearing out Ardan's Peaks and Taron Mines. It's funny how we all play differently. I never used Resurrect at all, and yet you seem to be using it extensively. I suppose this is because Paladin starts with this spell? Also, I don't like Order spells, even though there are a few I would get.
But we agree on units it would seem. I have finally settled on 5 units that do the job together very well:
Griffins
Royal Snakes
Orc Shamans
Demonesses (with Anga's Ring equipped)
Royal Thorns
This team is good because you have a lot of speed and versatility, and plenty of scope for spawning stuff and generally controlling the enemy. Basically I use the spawned Thorns and totems as the bait and the Griffins and Snakes as the stick.
There are also no human units here, which is good because they would have terrible morale as I don't have Tolerance to undead/demon creatures. This is not really needed anyway - later I prefer an entirely demonic army.
The only two spells I am really using is Ice Snake (3000 damage to central hex) and Sacrifice. The way I am using Sacrifice is by buying a big stack of 500 Miners (which is only 20,000 gold) and cycling my 5 real units through the reserve system. The Miners will get terrible morale from the Demonesses but I don't really care - they are just in the fight to be sacrificed anyway (and absorb some hits if necessary). After you complete Tom Digor's quest he has a horde of these for sale, and they are so cheap. This way I am able to replenish my stacks of hard to find creatures, especially the Thorns. In fact I am loathe to go back to Darion just to top up on Griffins/Royal Snakes so I am using Sacrifice for them as well.
EDIT: looking at your screenshot there I am interested to see you putting a lot of runes into the Might school. I think I only have about the first 3 or 4 things (but I am a Mage, I know). You will need to save some more money though, 93k is not much for this stage (although I see you have the bag of coins worth 80k to sell). At the same stage I have over 800k.