How do you determine what kind of armor you could/shoud wear??

I am I ninja with some mage skills

I am proud to see that half of the threads on page one are mine

Well its a complicated subject.

Some armor you can not wear because you need x amount of strength, but that should be easy to see.

what you are trying to do is max out your 5 resistances (physical,fire,cold,poison,energy) these are capped at 70 so the best suit that you could assemble would be 70/70/70/70/70 and its on your paperdoll so you can see where you are at.

Now the complex part comes when you start adding mods to the armor. Lets use one most people use/want on armor: LRC (which stands for Lower Reagent Cost) the max for this mod on one piece is 20% so if you can assemble a suit that totals 100% LRC it would allow your character wearing that suit to cast spells without reagents. Cool you say, well armor pieces with this mod have lower resistances than pieces without mods. There are many other mods, the more mods on the armor pieces the lower the resistances will be on that piece.

The trick is to try to figure out what mod or mods you want on your armor, then try to assemble the best suit possible. There are quite a few mods, there might be a list here, or check uostratics.com, I know there is a list there. For now while you are getting use to your character just try to max out your resistances, you can always add pieces as you loot them or buy them from other players, once you get more familiar with the system, and you decide what exactly you want on your pieces.

You are also going to either have to make one of your characters a blacksmith and tailor to repair your weapons and armor because they do wear out. Or you can buy repair deeds from player vendors (price varies from shard to shard) with these you can repair without being a blacksmith or tailor but you need to be in a blacksmith shop or tailor shop to use them (there are other repair deeds, but these are the most used it depends on what weapons and armor you use)

Being a ninja/mage you probably want leather armor, because:
1) Studded Leather and Metal makes stealthing more difficult
2) Studded Leather and Metal block Meditation (Mana Regeneration Skill)

Aye go for leather as thats meddable so will help with mana regen. Then concentrate on powers attached to the suit once you have a good set of resists across the board (60 plus in all catagories).