Well, you should play a normal game for starters, to get the hang of the new King's Bounty, see the new mechanics, etc. You should also be aware that KBAP gives less gold than KBTL on hard and impossible difficulties.
What I can propose is that you start a paladin on normal, make sure you do as many no-loss victories. If you can't get a no-loss victory, consider your army setup and battle tactics and try to improve both of those. Also, getting a lvl 3 resurrection skill will greatly help you with the gold, provided you can get that far.
If you are bent on rerolling, as a warrior, you will have a bit easier time. If you reroll a mage, you will have twice the problems you had with the paladin, even on normal. It is up to you
