Personally, I would continue with the laminating as there is nothing sweeter than applying art to a laminated surface. Just order the 13/16" and be done with it or stick with the 3/4" and apply one of the suggestions.
If your going to paint, however, make sure to prime and use acrylic based (try to avoid latex paint as the ---steaming pile of meadow muffin--- seems to take forever to cure). Use a gloss paint as it provides the best adhesion. As for colour, if you have lots of light colours in your art, I would go white as it will help to keep your whites and primary colours bright. If art is dark and mostly black, then paint black.
Some might chime in and say you don't need paint, just apply directly to the MDF. I wouldn't do it, but lots have had luck with no paint and considering you will have plexi holding it down, there is no chance of lifting. In fact, lots of builders have applied non-adhesive artwork and relied on the plexi to hold it down. But this is not a good option in my opinion as even with the plexi holding it down, it is still possible to see ripples or bubbles.
Let us know what you end up doing
