1) It would work like a normal char, you have the option to put rp posts to learn jutsus for your NPC missing nin or IG. (Bio of course needed after DM Approval, so we can keep tabs on how many there are)
2) How powerful, is limited -only- to the 200 token ability, the npc tokens there after are for stats / items / weapons / Jutsus etc. only. (No extra slots after 2)
3) NPCs could have relations with other chars upon creation or via RP forums, but nothing IG (IE: NPCs going as Suna nin, and staying suna nin for a while before leaving. That would take the point out of being an NPC Missing nin, and just a free extra toon)
4) Unfortunately any rewards the NPC gains, will be limited to only that NPC (Not useable to player's other characters) This is to prevent confusion and issues upon refunds or deaths or anything like that for us. (Its best to keep PC earned tokens to PC based chars, and NPC earned tokens to NPC chars.)
Overall, yes I do hope people will enjoy this new option to play. It is like playing an extra Toon, with capabilities to make their own factions, and influence current political / plot as well. So it requires alot of responsibility, but I know that most of us are capable of handling this privilege.