The Community Patch Team mostly worked on the broken melee combat so the basics for creating a strong mage are the same. Get Learn Quickly and Mana Regeneration as soon as possible and the game will be a breeze. Beware though, getting Mana Regeneration early is quite possible ( I think I managed to around level ~20) but if used right can make the game terribly easy.

With Alternative Balancing enabled you will be required to meet some prerequisites before learning skills . For example you have to get Learn Quickly before getting Mana Regeneration and having the latter is required to learn Fire Mage or the spell Light is required if you want to get Fireball. I believe the patches also change the required stats for some skills.

For what I remember spamming low level spells like Fireball or Ice Lance instead of Fire Rain etc worked much better in the unpatched Gothic 3 as the high level spell took very long to cast which made them impractical. I think the Community Patch team tried to address that by changing the area that some high level spell effected from near the Nameless to near the targeted enemy. I don't recall testing it but getting better spells should be more rewarding with the Community Patch.

You can find a manual here which should give you a better idea of what I mean.

Finally, if this is not your first time with Gothic 3 I would suggest, without any doubt, installing Quest Packet 4.2 and the latest Content Mod (2.2 was the version I used). The difficulty may be much higher but if you make your choices carefully the game will be a much better experience, not unlike the earlier Gothics.