How many differen runes can be applied to one peice of armour?

See above for question

I want to add some Major warrior runes to my armour, and then use Minor Vigor to mostly negate the loss in HP, and then use grip of fortitude to gain a slight positive boost. Before I do all this though, I need to know how many runes can be attatched to one piece of amour.

1 rune for each piece of armor

Ouch... that's not so good.

therefore altogether you have 5 runes you can equip, Headgear, armour, legs, hands, feet

If you mean by one peice of armour a headslot for example then only one rune can be attached. Any rune applied after that rune will replace the original one on it.

For the attribute armours like most head slot items they will have a +1 attribute to a particular attribute tree and with the included "(stacking)" modifier, this mean's that putting a +3 rune of the same attribute will mean you'll recieve a total of 4 attributes from that item.

In the case of adding a +3 rune of an attribute to a peice of armour when any other peice of your armour has the same +3 rune the only effect that will apply will be the addition of the minus health from the rune.

edit: mmmm, bit late formulating my response...*runs away to hide*

Why do I get the idea that you're thinking that more than one vigor rune will give you more health than just one? You'll only receive the benefit of only one, that one being the highest rated vigor rune you've applied. As with all runes, they do not stack one on top of the other. But they will stack with Armor buffs:

Executioners helm: (+1 Axe) with one Sup. Axe Mastery (+3) = Axe mastery +4

Executioners helm: Axe with TWO Sup. Axe Mastery (still only +3) = Axe mastery +4