Been making my own fun mtg based templates and been working on my own card game. I have found it easier to make all my templates parts (full card colors, p/t boxes, and new masks) then fit the code on top. I mostly just find the template that matches what I am trying to do and re-engineer the code to what I want to do. But I also have like every template every made downloaded as a code base including flip planeswalker the one I did the templating for in High School.
Here's the tutorial I used to start out with, by green_meep from the old forums. It's from 2012 but still works pretty well all things considered, though I'd heavily recommend you download the full files ahead of time and use them for reference as you go as some of the instructions aren't always crystal clear. Also helps if you've got some programming familiarity already. After doing this I found squinting at other current templates for long periods of time was helpful to learn things beyond the scope of this initial walkthrough. Good luck!