Leave the check box "can be equipped " checked, or nobody will be allowed to equip it.
As far as defense, you could make an armor attribute and then use blocks like...
Change attribute armor by 20
change attribute armor by -20
(Or instead of "change attribute" you can do SET to A+B and A-B).
Then when you're hit by an enemy, you need to use a damage resistance formula
I made THIS FORMULA few months ago, feel free to use it.
Lastly, as far as restricting your equipment, you have two options.
1) Modify the button to do what you want (CLICK HERE to go to my Text tutorial on how to do this)
2) unequip the item ON EQUIP if the player is the wrong class.
I will be recording an updated video tutorial on how to do this, but it's video #14 in my upcoming tutorial series so it might be a minute.