I don't think you can have a castrandom in the same macro as a castsequence, unless you include modifiers... because they might both try to fire off a spell at the same time.

I know you can have multiple castsequences in the same macro, provided your pauses are set up appropriately, so you never have more then one spell firing off at once... A priest could:

/castsequence [target=party1target] reset=target Shadow Word: Pain,,,,
/castsequence [target=TankName] reset=target ,Renew,,,,Renew