@James: Haha. I'm by no means an expert player myself but I do have read some stuff in these boards. Most notably reports like I just wrote and nation guides (I especially recommend those written by Baalz, I find them fundamentally educating). The spell range calculation was pretty extreme for me too, I certainly don't do it normally, but this battle was so important I wanted to have every advantage I could think of.
For upkeep my own rule thumb is as long as your upkeep is less than ~40% of your total income, you're doing great. More than that and you're starting to have increasing trouble getting money for new forts/temples/labs or replacing those that got destroyed. Of course sometimes, most notably during war, you just need those troops and upkeep gets high but that's the time you save gold in other pursuits.
For research/battle I aim to have as low number of mages in the battlefield as humanly possible to minimize the research loss but I usually make those mages count. In battle a single power mage is way stronger than dozen crappy ones imo. Also, use the most cost effective mages for research, that is the one with the lowest cost/upkeep/research value ratio, because it saves money in the long run. For any particular mage I consider this ratio good if it is equal or less than 0.8. For example EA Ermor Augur Elder has cost of 250 gold, upkeep 16.7 gold/turn (250/15) and base research value of 8 iirc. So for him the ratio is ~2.1, not very good. However he is very good battle mage/item forger/ritual caster so you should use him for more those kind of tasks and less on research. EA Ermor also has Flamen 120 gold, upkeep 4 gold, research value 4 sacred mage. His ratio is exactly 1, which is not super but way better than the Elder for research job, no? If you took magic scale 1, the Flamen's ratio improves to the target number of 0.8.
For mage improvement find ways to create magic path boosters(for ritual caster and later on for battle casters) and use booster spells in battle (summon earth/phoenix/storm etc power). They make a huge difference in mage perfomance. I hope some of this was helpful and not some crystal clear rambling.
I 110% agree with you that the better understanding of the game you have, the more enjoyable it becomes.
@Karlem: Glad you found it a good reading.
I ran some simple tests in SP and Dust to Dust worked fine then. My PoD has a pretty good precision and there's no way a master lich can survive 22+ damage, no MR, armor negating punch if it hits. You're right about more death mages being more safe choice but I don't have so many of them to begin with and moving them to front lines would have taken many turns, more time was something I didn't want to give to Jomon. Afterall I got this master idea just previous turn when I was brainstorming ideas for how to bybass the mind duel. The communion Jomon had was for Power of the Spheres to boost the slaves so they could throw Blade Wind, it wasn't important for the duel itself. Now that I think more carefully the master lich's levels were in fact boosted by the spell and not by empowering, so a slight error on my report there. This means my loss in the mind duel is even more bitter but now I do get to erase the props I gave to Wazooking earlier.

Yep, I know mind duel is only affected by base astral skill, can't speak for Jomon though.
My prediction about Midgård upkeep is based on the fact Aezeal advertised having found a sage guild some time ago in this thread. Midgård has pretty horrible national mages for research but sages have high research. If he has bought a lot of sages, it would explain his great research accumulation but sages are pretty high upkeep mages (and therefore not very cost effective), which would translate into money issues. Especially so because Midgård has had its share of conflicts and province losses, which have reduced Midgård's income. It would actually be pretty interesting to know if Aezeal could confirm whether or not my theory is correct.