Worked on textbox layering - it's possible to view multiple textboxes at once, if you are in a conversation and walk in range of a different one. Design-wise, this isn't quite what I want. The intention is for there to only be one conversation on screen at a time. But in lieu of enforcing that design constraint, I've made it so that only the textbox for the nearest conversation is visible.
I started drawing textures but that was painful and since I'm only making smallish 2D sprites I think I can get away with basic materials and procedural textures (like the camo texture here). Anyway, I'm pretty happy with this result for now and I think I'll follow this process for at least the next few buildings I need to make.