Custom decals/printing: where to start?

[TeddytheSpoon]

I'm approaching the finish line with a LEGO train design of an LMS Ivatt 2-6-2T 2MT - just waiting for Breckland Bricks to re-open so I can ask about custom wheels. But having built most of it in the brick already, I'm starting to wonder if I should add some custom bits for the livery too.

Does anyone here have good resources for how to get started on this? I've considered having some parts printed, but wondering if decals might be a better option for price and re-usability of the parts. (It's mostly tiles that would need doing, at least for this one.) I don't really know much about what process is best or how to do it though!