Walkthrough for the "Tribes of the East" expansion.

Guys, please help me out. I'm currently finishing the last mission of the second campaign. I just need to capture that mega-evil magic castle and then defeat Alaric.
I apologize in advance if the question is silly :)
I understand that if I defeat the castle with Gothar, then I'll have a very, very long way to go to reach Alaric. So, is it worth it to gather magical troops with a secondary hero and meet Alaric with them (i.e., not with Gothar)? What kind of troops does Alaric have?
It's impossible to defeat the city with magical troops; they tear me apart after the third round...