Lowest dominion I ever won with was 1 on Old world, Ulm, all nations, all AI set to impossible, max province strength, extra points from lack of dominion into a strong rainbow mage. That was a _great_ game. Lots of hanging on by the skin of your teeth, summoned critter mobs from hell (ie huge battles with 2000 plus on each side), running away like mad to keep my pretender out of combat.
The trick, as much as there is a trick to anything with as many variables as dom, is to focus on raising your dominion every chance you get (ie temple in every territory, high province defence, preaching in every province with a swarm of crappy priests). Also, get conjuration high as soon as possible. You want summon leaders that can make minions, not one shot summons that create a finite set of strong criters (ie summer lions). The summer lions are needed at the begining for surving until conjuration 7, but shouldn't be used much afterwards. Also, don't waste gems in this sort of game with spell searching, move your pretender to search (I mentioned a strong rainbow mage
. All of your gems need to go into summoning criters. Your gold once you hit your stride goes into funding your swarm of crappy priest groupies (in the end game I was moving around stacks of 100+ rank two priests) and buying province defense (to keep the AI from using it's random swarm rampage attack on you).
Another thing about this sort of game is that you end up really paying attention to the other prenteder's dominions. When I play a low dominion game I end up in the end game having special purpose armies depending on the dominion of the pretender I'm attacking (ie cold resistant, heat resistant, don't need food, etc.).
Well, enough rambling