There isn't enough experience points to max out all stats, so use them wisely. (You need 5000. They only give you 3455) I recommend maxing Mana and getting your Control to as high as you are comfortable with. Health is not really important if you are a "summoning" wizard as your creatures will take the hits for you. Just don't wander too close to an enemy wizard who has powerful attack spells.
In the Mountains of Cader Idris, just make sure you go slow. You might have to go through this stage a few times just to get the general layout.
Another tough stage is the Azorian Mountains. It's possible to do it the easy way and the hard way. Remember your key objectives (forgive the pun). Get the keys and get out. Killing everyone is not an objective. In fact, the storm giants and centaurs respawn constantly. However, if you opt for the easy way, you'll miss a lot of good items. I did it the hard way first time round ie. I fortified all POPs. VERY TOUGH. But it was worth it, in my opinion.
If you're wondering how to open that last chest in the Initiates Training Chamber, my hint is to make sure you explore EVERY SINGLE BIT OF AREA. Get rid of every single bit of fog. If you still can't get it, just ask me. By the way, it's not worth your while to actually open the chest. You'll only get a feeling of satisfaction and annoyance at the whole thing.