Roughly trial & error, here. Any campaign that syncs to sfdc is delayed 15 min (we started at 5, then 10, now 15) in order for all campaigns to run. Now, that being said, the only thing we have to wait for is the sync; we don't have dependent triggers that need to fire in order. I would test with wait steps in each to make sure they wait long enough for the previous trigger to finish; but there isn't going to be a scientific or perfect answer...
Seconding what JD said. Since the "Request Campaign" is both incredibly powerful and yet also considered very low priority by Marketo (no clue why), wait steps are the way to go here. Setting up rules the way JD has done is the safest route since you know it'll take some time for all the triggers to fire, and adding the wait step as the first action in the flow will allow you to control the order of operations.
My wait steps are much more aggressive, giving pauses of 2, 5, and 10 minutes, but it's essentially the same exact concept.
Kudos, JD Nelson!