I don't use PS/PSE so this many not be helpful at all
It very much depends on the template:
- if the template is a clean and simple style, with the papers/elements pretty much centered in the page or off to one half, it is quite straightforward. I would crop all of it in one go to a 8x12 which captures all the elements/papers (a good example would be the April 2022 Mojo Perks template)
- if the template papers/elements spread all over the 12x12, it very much depends on the template. For some I'd still try to crop to a 8x12 after I have shifted the elements which fall outside of the 8x12 more to the center (example: I'd do that for Michelle's template challenge this month). For other templates, I'd resize to 8x8 and then increase my canvas size to 8x12 and move elements further up and down to fill upward and downward. It really depends on the general orientation of the template.