There are no restrictions on what one can wear, wield or hold; or who one may group with, but there are consequences. You want to be a thief and wear that fancy looking scale mail? Feel free, but don't expect to ever be successful at sneaking around, or stealing without being noticed. Become a mage and wear full plate? Sure, can do, why not? Of course, it would be wise not to try to cast a spell. All of the magical energy will be trapped inside your armor and cause a melt-down, turning you into a pile of slag and ashes.
Multiplaying is allowed, that is have as many characters as you like. Don't sign on with more than one at a time though, except for one special circumstance; Twins are allowed. Create two similarly named characters (of the same race, of course) at the same time and keep them within 1 level of each other, or only sign on with one until they are within range again. Some of the twins currently populating Continents are: Tear and Tier, Terone and Tyrone, Time and Thyme, Uod and Uoduod (they are giants and not very creative with names :).
PK is limited to those who are signed up to participate. All those selecting Vampire, Werewolf, or Drow race or Ninja or Thief class are automatically PK registered.