With my warrior I had lots of mana from equipment bonuses, going with about 2 parts strength, 2 parts agility and 1 part constitution, on average (boosted constitution more earlier in the game, until it got high enough I was fine just relying on equipment for much of my hit points). Charms would have likely given plenty of mana for a battle mage, though I also built up many more
restoration potions than I needed.
For a maximum, yes 90 should be fine. Just before fighting the Demon of Lies, my stats were as follows (the number in brackets indicates the values with no equipment, without Finnigan's lockpicks in my inventory).
Level 53 Warrior
Vitality 1260 (444)
Magic 574 (30)
Strength 145 (111)
Agility 150 (112)
Intelligence 18 (10)
Constitution 100 (74)
Offense 124 (89)
Defense 108 (78)
Damage 139-178 (54-64)
Armour 484 (0)
Lightning Resistance 95 (25)
Fire Resistance 110 (25)
Poison Resistance 35 (25)
Spirit Resistance 95 (25)
Reputation 51
Weight 4500 (3820)
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