Useful tip for early game(before level 20) getting the band of scouts gives you 1000 extra "spies" for 24 hours which means you can see the full army size of most of the kingdoms your level and they can't tell how many units you have in your kingdom(ergo less likely to attack) not bad for 3 gems. Happy hunting
Just for fun(after beating the game three time) I restart and deliberately lost every duel. I spent every month training, joined neither faction, and refused to interfere in anything or collect any items. At the end the Grand mage challenged me and I whupped his ass. Afterward I went on to become this legendary hermit. This game rocks!!!
The only melee unit I found useful is the cutpurse/gentleman because they steal gold(I wish the gold went straight into your treasury instead of the battle funds where you lose most of it at the end though). Also maybe you can increase the difficulty by having heros 'die' if you lose a map and you have to recruit them again. Great game!
 "Hordes of Hordes"){kind=icon}
 "Utopia Kingdoms"){kind=icon}
 "Arkandian Crusade"){kind=icon}
 "Book of Mages: The Dark Times"){kind=icon}
 "Protector IV"){kind=icon}