Cloth and Leather. That's it.

Base form is Leather, but all 3 trees can increase your base armor:

Balance: You'll likely be moonkin after level 40, which makes you more like a shaman, but with a mage's dps. Moonkin shifts your armor up to the likes of mail.

Bear Form: Level 10, increases armor to the value of mail and stamina slightly, making you like a warrior with warrior related spells.

Dire Bear Form: Level 40, moves your armor up to plate value, and increases your stamina greatly. Fantastic for tanking.

Tree of Life/Travel Forms, and your regular form: Restoration grants a talent that boosts your armor in between leather and mail, but close to mail and your travel form and regular form the same way.

Cat Form: This form keeps the same armor, so its like the rogue, armor and everything.

Order of Armor Value:

Cat Form; Leather (rogue armor)

Travel Form and normal Form; less then Mail, more then leather.

Tree of Life Form; slightly less then mail. (near shaman)

Moonkin Form; Mail (shaman)

Bear Form; Mail (low level warrior)

Dire Bear Form; Plate (High level warrior)

No - Light armor is leather, cloth, etc.

Plate armor is considered heavy armor.

depends on your opinion

level 99 dungeoneering equipment exists when you are in a dungeon

dungeoneering is also the only skill which goes higher than 99

However outside of a controlled environment there is no armor that is higher than 80

So the facts say that

a) jagex would need to increase the the combat level cap

b) create an armor and ban/make rules about it for pvp

If you mean what armor should a level 100 get the obvious choise if free to play is full rune with fist of guthix gauntlets and kite shield

memmbers have the barrows, vesta's, bandos and void to choose from

i recommend void for training with overhead prayers and bandos on anything else

but pvp should be rune whip/dds or hybriding barrows or vesta's degrading pvp armor

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Roman body armor, as all other body armor, was used to protect the body.

Combat armor is for melee while drudic armor is for mage.