These spells are worth considering:
pestilence - something nasty for the inital handshake
summon eagle - to scout the landscape
summon minotaur - to attack and defend PoPs
totem of resurrection - to support PoPs
As you enter the realm, the wizard will approach you and a cut scene will start.
Escape out of the conversation and cast pestilence on him (make sure that it sticks) before he walks off.
Summon an eagle to scout the landscape.
Attack the northern PoPs first with minotaurs,
and support them with totems of resurrection summoned to the north side of the mana wells.
Don't bother speaking to these, as they will all simply mumble.
No useful information can be gained.
kill the wizard
When you've maxed your creature count, send 5 minotaurs to kill the enemy wizard,
located on the alter in the bottom-left of the map.
They'll take out the chaos emplacements too.
From where the wizard dies, collect the key, and release gaion from her holding cell.
Gaion will be heavily injured and bandaged.
There are no cool objects to collect from the map. Therefore there's no point in scouting.
Once the portal appears, just leave it.