You might want to make sure that the pump is turned OFF each time before the multi-port valve position is changed. Trying to move it with the pump ON can damage the gasket, cause it to not seat properly, and could cause some sand to escape the filter. Also, it is a good idea after backwashing the filter to put it into rinse for a few seconds, before going back to filter mode. Some pool cleaning people might not be aware of the damage that can be done leaving the pump ON, or afraid to turn it OFF, (lest it not start again,) to backwash the filter after vacuuming.
Even though you may have a slightly larger pump then is most electrically efficient, your filter is certainly large enough to handle the pump output, and should not have been "over-powered" by it. The laterals inside of the filter are buried in (and supported by) sand, and it would be very unusual for one to have broken from just pump pressure. If it was broken from the beginning, then you would have had sand outflow from start-up. More likely is that too much sand was put in the filter (or vacuumed up,) and some of the excess just got carried out during backwash, was not rinsed out, and then went into the pool on filter re-start. At least, I hope that is all that happened!
As frankthailand noted, you'll want to keep the circulation and SWG running to ward off water stagnation problems.
Best Wishes, and Good Luck!!!