A tile mural sounds great! But I'm not sure I'd want to hide it behind a tank & plants after all your work & artistic talent. Maybe an above the tank mural leading down to your tank? The ceiling's the limit for height

. Fake paludarium with a mermaid perched on rocks, maybe a waterfall, then underwater scene? (OK, I don't really know the story, can you tell?) We going to need to see what you come up with!
All I can say is if you go with above the tank art, think about how you'll hang it BEFORE the tank is in place. A friend gave us a large painting that would be great above our 75g...but there's no way to lean over far enough & high enough to hang it without moving the tank (no trivial chore as I know you know. A few inches or miles, it's a tank tear down either way). Think about the weight of tile too. Stick it to the wall? Or to plywood & hang it somehow...Geez, it could be awesome!...eventually...Just the art alone could take...a long while before you even get to the tank proper. Or just paint the mural on the wall or canvas & skip the tile?
Go for it, or divide it into 2 projects; the mural & the tank...& the planting & the fish...yeah, ok, a few projects but fun 1s!!