Well the best thing to do is to look at the tailor and blacksmith, look at what stats the better weapons and armor needs and go for making those stats. Being a magic user you will be putting most into your magic some of the high level weapons for your class need magic as high as 300+
I should add, however, that you shouldn't invest in Blessing of the Purehearted at all, beyond the single prerequisite point. Ironheart Blessing is the one you want to max out as soon as you can. Purehearted is an inefficient heal, whereas IB is heal-over-time, and stackable, making it much easier to keep on a tank.
You should aim to put at least 1 Con/Vit every time you level up. A cleric needs to be able to stand it's own in battle. The Cleric is the class with the revive, and therefore must take special care not to die. It's also the class that must look after the tank. This means the Cleric must be able to look after themselves and the tank to some degree. This will require a decent amount of defense. The Cleric's defense is health, since it can heal it pretty quickly. This is Vitality. Never worry about strength for anything beyond equipment requirements and basically ignore dexterity. Dexterity should only play a part in the clerics role in the late-game whereas it may be required for PKing.
The Cleric, unfortunately, can pull the aggro of monsters by healing a team mate currently being attacked (usually chased) by them. This effectively means that a cleric must be able to tank beyond what other non-tanking classes can. Most of this ability will come with the Plume Sheild, but without a decent amount of hp to play with as well, you're gonna have a lot of pressure to keep your mana supplies right up.
The further you get in the game, the more Vitality you should aim to put into your character as well. This is because you will be doing more Call of Duty's, HH runs, bosses and a bit more grinding. Death is a common occurence in these areas of the game, and the exp loss from dieing becomes significant.
-Con is important for a Cleric. Dexterity plays no part in a Cleric's build til late-game.
-Clerics should be able to tank temporarily in a gone-awry situation.
-Clerics must take special care not to die. In a squad, death affects them more.
-Clerics need more Con and general defense towards the end-game. This is where light-armour can be a worthy option.