I highly recommend the Craftsy course, Machine Quilting with Templates by Kimmy Brunner.
I've bought far more templates than I actually use, so I would start out with just a few. Different size circles are helpful, as are ovals. I also like using a heart occasionally. You need at least one straight line template in addition to your crosshatch system. I wouldn't bother with triangles or diamonds since you can do them with straight lines. I don't care for the nested rulers, but I do have a set (spiderweb shape) and I use them only occasionally. I didn't find that it was difficult to do ruler work, and I do only that and free motion - no computerized quilting (although I would love to have that available) and no pantographs. I use the straight rulers extensively for SITD. I also don't care for the rulers with handles on them, but some people love them. That's another reason to buy cautiously until you find out whether you like ruler work, and what types of rulers you prefer.