@rkm i love thumbs forward but I agree - anatomy and personal preference. some of my clients do thumbs forward and some thumbs back and some are a neutral grip. gotta play around with it to see what feels best with your body.
@ulfric I teach kettlebell classes and everything I teach can be modified to a beginners level!
Just go for it, let the instructor know you're pretty new and if they're good they'll help you with any adjustments you need.