Not sure where I stand with this? Do you need formal training? Not sure? Do you need instruction of some sort? Sure do...whether it be from observation/application.....video instruction/application.....or a formal class. You do need to be at the very least "demonstrated" the proper way to cast a flyline.
That being said, it's always a learning process. I doubt anybody is as good now as they could be tomorrow. We can all improve our casting in some way. Some of which can only happen on the stream in fishing situations however. I learned by observations and mimicking. Got better with Mel Kreigers video and further mimicking. And then worked on it on the water over the years. I later took a class out of curiosity and learned some neat techniques that i still apply as well. Always learning.
Grips? There are some I prefer. My favorite is the grip on my Orvis Far-and-fine. Other I don't like probably because they don't fit my hand and I just plain old don't cast as well with them. I lean toward a full wells but in a much shorter and slimmer version. And although my hands are smaller, don't care for the ultra-slim cigar grips that are common. But I cast at times with my index finger pointing...at times with my thumb extended....and at times with a normal grip. I don't cast in the classic 10-2 stroke though & I break my wrist alot on purpose:^) Steeple casts, dump casts & sidearm casts don't lend to classic instruction all that well:^)