well seekers and i have been playing a bit and what i can say about mana problems now is that sometimes it can be good to not invest all points into a skill, even if the scaling is somewhat linear but increases a little (with some skills there is not high change in damage:manacost ratio with points invested) and instead cast more, but weaker spells. the best mana cost is when you can drink mana pot, cast, and the mana will neither fill to 100% nor drop below spell cost, so you use the mana pot at its highest potential
ive also tried to put eth runes in armor sockets for 20% mana regen and its useful for mana but for tankiness it seems better to get flat damage reduction from diamonds and progress in game for more lvls and better gear later.
at lvl 37 there are lum runes for 10mana 10energy 15% mana regen which helps even just 2 or 3 of them in sockets and the rest diamonds. could do all mana regen but wait till you go in a place like a3 and you get oneshot by some mobs because 0 damage reduce, diamonds help with that
and ofc merc same thing, damage reduce makes him tank it better
and best items for many casters is arcanna set. gives mana and teleport and other good things. griswold is best place to farm sets afaik (often drops 2-3 set items but sometimes none), or at level 14 or so the gamble price for long staff is almost the same price you can sell it for again so its easy to gamble the staff then