1) Shadowpriests do not have a "reliable" dps rotation due to different dot durations and cooldowns. It's the nature of the spec. You basically just keep a "priority list" of "VT needs to always be up, always have a pain up, MB every cooldown, VE when threat isn't an issue and aoe damage, Death when health is high and no chance of dying, Mind flay when you have nothing else to do".

2) Check out this blog post I made a little while ago regarding pairing up different classes/roles for multiboxing. It might give you some insight into how you can match up the abilties of your different classes.
http://vboxing.net/v/index.php?q=node/96