In order to keep contacts out of the certain flow, you’ll head into the Flow Filters for your trigger metric and add in certain exclusions.

So for Abandoned Cart, you’d put in a filter - Placed Order Zero Times Since Starting This Flow. That way all of those who convert, don’t stay in the flow and then ideally they are then triggering into your Post-Purchase flow.

Same for Created an Account. If that is like a Welcome Flow, you’d add in flow filters to your other two flows to only allow contacts created at least 10 days ago to enter in. That way if your welcome flow lasts 9 days, on day 10 they then would be able to start triggering those other flows. 

Smart Sending can also help if you do have some cross-over of flows but the filters will help keep it siloed.