I love your creations and you are way ahead of where I was when I first started. What's neat about tombstone building is that every year the bar get raised higher and then they show how it done. That, in turn helps others build on the knowledge learned. Haunters are the most amazing people.
Many times I use acrylic paint (artists' paints) for details after it was base coated with Drylok. Because you used exterior latex paint that would give it the same protection so you are good there. I've never had problem with the details paint effects washing away so you shouldn't be concerned. You are good to go :)