Ingredient guidance pls... plain yogurt, is that Greek yogurt? Neutral oil... would that be light olive oil? Butter... unsalted? Eeeeep.

I think that any unsweetened, unflavoured yogurt would work. Greek yogurt is thicker, so I would add a tiny bit of water to equal the consistency of plain yogurt.
I use canola and grapeseed oil for neutral flavoured oils as they have a higher smoking temperature than olive oil. Grapeseed is much lighter, when I want to substitute butter in a recipe, I find avocado oil works very well.
I would use unsalted butter in this recipe but if it is unspecified in the recipe, salted should work as well.