I dont know how it was in skyrim etc but is it usefull to wear heavy armor as caster ?

Got Cloth armor, Int? medium armor, Dex? heavy armor, strenght? How items look like in teso ? any informations here ?

If you want more defensive stats and don't mind sacrificing some magicka, then yes.

http://tamrielfoundry.com/

You will find a lot of information there.

Light = Magic

Medium = best for rouge type chars

Heavy = Tank

I am planing on playing a mage type char. So I going to do a mix of the 3 types of armor. Paws and Feet will be light for best magicka, Chest will be heavy for better protection and head will be medium for running and avoiding attacks. The becomes, does want to be a pure mage and get every item to max that role or trade off mage type items to become a "jack of all trades" idea?

dont forget that you can also mix and match. maybe you will go half and half so you get some magicka bonus and some higher survivability. i am also considering wearing different armor in pvp than i will in pve, will need to see how it plays out though

So long as you don't want the 5 piece bonus passive from any armor set. You could go 3H,2M,2L if you felt like it.

to me thats what it comes down to, what bonus do you want. if that 5 piece bonus is a must have then i would go 5/2 if not then mix it up a bit more. i personally see 5/2 being the way to go though

Yup.
They use different names but "What's in a name anyway?!".

Afaik there are no set-effects so you are free to mix and match, but the passives from the armor lines get stronger the more armor of the given armor type you wear.

10% spell crit, 25% decreased snare duration, 4% less damage taken.
I don't know if I'd call this a must have, since you have to pay a skill point after all.

In the end it comes down to play style,For two of my casters heavy armor was needed but that is my preference and style for those two. Just do what you want.