Playing, and focus everything of mana and INT
 

If you play as a Mage, would it be good to put every opportunity to raise INT and mana.

I want to have INT to be over 45 and mana over 120 toward level 25-26.

Right now I am playing a Mage at level 25 but I find that my level 3 chaos spell only do 1500-2500.
That is pretty weak. I have INT, Attack, and Defense only in the 12-16 because I devided out among the three too much.

I got beaten up badly when I reached demonis.

Well that's becouse you can't always chose INT at level ups, and items are random so + INT items are not guaranteed to be found. My first game was as a offensive spells oriented mage, and i must say it's not the best idea. Focusing on mana&spells means your army is weak, and spells do not scale like leadership. Eg. it's better to give archers some dragon arrows than to cast offensive spell, not mentioning creatures resistances against magic.

It is completely possible to achieve high int and mana while still getting good combat stats. You need a little luck with items, and some smart playing (like having no kids with Feanora), but it is doable. Attached is a screenshot from my last mage game almost at the end. Note my stats: 20/14/42 att/def/int. The better attack spells unleashed some serious damage. I think fire rain was 6-8k damage, something like that, and lightning did aa very nice amount as well, though the numbers escape me atm. But a high int mage with good combat stats is totally possible!

Oooh.. impressive. That's quite a good set of items there. I'm excited to try out a mage for my next game, and your character there is essentially what I hope to build.