Great 
So, you could create a BP_Door class, give it a custom event that will open it. Add a BP_Door variable in BP_BlockController, click the eye symbol to make it public. Then place a door in your level, and click the BP_BlockController, set the Door variable to point to your Door.
Where the AllPlaced correct print string is in your BP_BlockController, get your door reference, drag off from it and call your Open Door event.
Doing the open door bit would be a separate question but there’s a lot of infoirmation on that online already too. Hopefully this will get you started.