Ok what i would suggest for the party is ,
1) there should be a total party level , all members gain xp , but only take the xp from 1 member for the party level, that's how to level it , when reached level 10 or so the party leader gets 1 party point and can use it for boosting the party or party heal or so wich he can use every 1-2 min or so but also on level 15 , 20 you get points so after a while you party gets really powerfull in boosting skills etc but when at those high boosting skills the cooldown gets more , after a while party will get powerfull and you can take on even stronger enemies
2) when in a guild you can still join a party , else it gets really difficult
3) when the monster drops money it gets devided under the players so,just an example : rabbit drops 100 gc when with 2 each get 50 , when with 5 each get 20 and so on , party system is mainly for xp not to get rich (my opinion) with items just let it be a random, then player 1 gets it then player 2 ..... maybe you can do this aswell for the money don't know
4)when multi attacking a monster i think the damage has to go to the guy who attacked first , or the weakest , weakest armor , one of those :p
5)for the xp i would just devide it like when you normally fight the monster alone you get 100 xp when at party you get 60-80 or so
6)party system should have a diffrent chat like the general/market channel just with @ but instead of white use yellow or so , so you can really see the difrrence between the party / general/market channel
7)party can only be created by a person that has arround same you need for guild + for creating party it costs 5 k or so , also you can only join a party when you reached a certain level else you have a level 70 and his friend is only 10 or so then he uber levels without having to heal or do anything
i think party should also be when party leader is 80 only levels 70-90 can join so all arround same levels
9) you can make few quests for party's like for completing the quest you need a party that is level 20 + and kill powerfull animal/monster together
Greetz Z