1.  Yes it can be done.  However, make sure you do not have an activity with only server events that executes continuously until the condition is met .  Normally for loopbacks you'll want to have some delay on the Start rule so the activity only fires once every hour or day to check for the matching conditions.  If your activity contains a Client event then a Start rule delay should not be required.

2.  No.  It requires custom code.  You would need to generate the code for that event and add some IF conditions about when to perform that particular event.

Depending on your scenario it may make sense to separate those events into a block of separate activities and then you could add Preceding rules on the activity to decide when that activity should start.  However, although this approach might save you from custom code the additional activities and configuring all the preceding rules and lines might not be worth it.

Many thanks