Good ideas but your not understanding how a persistent world server works (technical name for an MMO). It's a huge database processing tens to hundreds of thousands of transactions per second. Your actions are nothing but transactions. There is a heartbeat timer that governs time, basically your attacks are just scheduled events taking place during a routine heartbeat. Things like parry / guard are just responses to the event of a monster hitting you, their not their own scheduled events. The way FFXI seems to work is they only allow one player event to be scheduled at any point in time. Now it ~can~ be made, with significant modification, so that multiple events per actor are scheduled and processed. I figure they did it this way for performance reasons.

Try not to think of the game as a pretty picture of you doing stuff but as the server processing ten thousand+ events per second and that everything you do is just an event the server process's.