Travelingoz: Buffs tick down every time your character takes an action. So take the Inquisitor's Holy Anger spell for instance. If they cast it on themselves, it immediately loses 1 turn duration because they apply it to themselves, then their action is concluded and the duration decreases. Much better to cast it on something that hasn't moved yet. You can stall the duration by waiting instead of defending, so it's quite often a good move to have your Royal Snakes wait, then buff them, and then they take their action at the very end of turn 1 and the beginning of turn 2.
How this applies to Mana Spring is that the duration goes down by 1 every time you are hit AND every time your unit takes an action. At the lower levels, Mana Spring doesn't last very long so it's hard to get a lot of mana out of it. At best, you put Mana Spring on a unit, attack with it and get counterattacked to refund the cost of the spell, and hopefully someone attacks you. Then it's gone. But at level 2 and 3 the duration increases to 4 and 5 respectively so there's some real potential to gain a lot of mana. My favorite is still to put a stack of summoned thorns in a poison cloud, because you are guaranteed the full return on your investment.
As for levels 1-9, I didn't do anything different than what I described in the first post. I also didn't take any leadership bonuses from leveling up until level 12 or so. For me the first 14 levels or so were the most "tactical" because I was frequently fighting strong or very strong opponents, but Darion is also the easiest continent so there's the most opportunity for strategy to pay off. When you get to the later levels the game is much more "brute force" because some stacks are just too big. I remember fighting a stack of 70 demons, it took at least 6 turns of all of my stacks focusing on them before I brought them down. I guess tossing totems and stone walls in the way is still strategy, but not like it was in the early levels.
As a mage on Impossible you may need to start taking leadership bonuses sooner, especially if you can't find Fire Rain. Either that or spend your early runes on the Glory skill.
I will look up my current stats and post them today. I can say that I don't feel like I have particularly good equipment. Having read about some of the items other people have found, I think I'm missing out in that department. Here's what I'm using (from memory):
Some Intellect Helmet (+3 INT, +1 Defense)
Pirate's Halberd (+3 Attack, +5% gold, from quest)
backup: Silver Rapier (+30% damage to undead) x2
backup: Adherent's Staff (+2 INT, +10% lightning damage)
backup: Pilgrim's Staff (+1 INT, saving the upgrade battle as a rage booster)
Slippery Cuirass (+2 Defense, +10% Physical Resistance)
Ogre's Sandals (+2 Defense, +1 Move for Giants and Ogres)
General's Baton (+750 Leadership)
Battle Shield (+2 Defense, +1 Attack)
Some Round Stone Artifact (+4 Defense, you can trade Magic Crystals for Stoneskin scrolls. I got it from the zombie in the Marsh, not sure if it's random or not)
backup: Silver Chain (+1 INT, -2 Defense to enemy undead)
Anga's Ruby (+300 Leadership, GIRL POWAH++)
I do not have a wife yet, mostly because I don't have any artifacts that I feel like I "have to have" but don't have slots for. I probably should have married Feanora early in the game, but since I didn't I'm just going to wait for the demoness in all her dual wielding glory. The undead lands should be much easier with 2 Silver Rapiers.
Also, another mana loop for fighting keepers. Originally I was of the philosophy that the friendly gremlins (brown) needed to die first because they continued to summon units. However, now I feel like the evil gremlins (red) should die instead, and you should hold a brown gremlin hostage to summon an endless supply of units for you to use Mana Spring on. As long as your army is strong enough to take control of the fight, the small # of allies one gremlin tower can summon will not be strong enough to beat your endless supply of summoned thorn stacks. However, I still can't upgrade my archmage's staff or baton without taking losses so I obviously need more practice.
Edit: Added Battle Shield, changed Colonel's Baton to General's Baton