Hello! Newbie here! My backyard is currently gravel… would it be okay to lay artificial grass on top of that, then a tarp, then the AGP?
Or do I need to clear all gravel?
What sort of gravel? Size and shape.

Is the gravel constrained, or free to shift around?
 
You will need to clear all the gravel. Otherwise, the floor of your pool will be lumpy bumpy, and you risk putting a hole in your liner.