I ran through the game once on normal in a couple days and died a couple times as a Mage. I mostly just screwed around but I wanted to do a second run through to get achievements like grabbing all the chinpokomon, and getting all the armor. I also wanted to beat the game on the hardest difficulty.

It ended up being easier than the first run through. I rarely ever used healing potions. And I usually killed my opponents with one blow. I'll share my set up.

I chose the Jew class. This could probably also work with Mage, but to a lesser effect. It definitely wouldn't work with Thief. I don't know anything about the Fighter/Warrior class.

Early game set up:
Outfit:
Level 3 Friars Cap
--Healing Patch that increases amount of health you heal (whichever one you have available)

Level 3 Friars Robes
--Leeching Patch that leeches enemy health when you attack

--Extra Slot, Later the Red Cross Patch (You gain 1 PP when you heal)
Level 3 Friars Gloves

--Extra Slot. Customize as needed.
Level 3 Mongolian Bow, Then Level 6 Broken Bottle
--Freezing or Shocking Patch

Best Melee Suited for Level

--Any Strap On, Preferably a defensive one

How you play:
You are almost never going to use your melee weapon, and you are pretty much always going to use your abilities, and in some situations your ranged attack to hit guys in back. You want to use weapons that do lots of attacks, that way you leech more HP and PP off your enemies.

Late game set up:

Any helmet that increases HP
--Red Cross Patch
Level 12 Bishop's Vestments
--Leeching Patch that leeches enemy health when you attack. (By 100)
--Healing Patch that increases amount of health you heal. (By 250)
Any gloves that increases HP
--Extra Slot. Customize as needed.
Level 14 Chakram 
--Vampirism Patch. Leeches health from bleeding targets.
Any Melee Weapon with 2 slots
--Patch that increases blocking ability by 15%
--Patch that increases blocking ability by 25%

How you play:
You are never going to use your melee or ranged attacks ever. As a jew, they are worthless. You have the plagues and whirling doom. With this mixture of patches, you can now spam plagues every single turn. Have plagues and whirling doom fully upgraded. The best thing about this combination of patches and armor is that every time you do your plagues you will fully restore your PP and HP to it's maximum. Also, when you cast plagues, never cast any plague that grants attack up to your party unless you really feel you have to. Always cast a plague that grants ability up. This is because your next plague is going to immediately gain that ability up. That and depending on who your buddy is, they will then likely have a x4 ability up on them on their turn. If your partner is cartman, you can easily finish off most opponents in one turn this way (even bosses), especially if you use your speed potions correctly. I killed Craig on hardcore before he even got a turn doing this.

You should never die if you use this formula.

Kudos did this on a Mage and Jew and worked like wonders.