I think it almost has to stop at very basic early versions of guns because if not they are going to make 80% of the combat fighting styles obsolete.
Preferably no guns tbh imo. Adding guns in a realistic medieval game is going to create balancing headaches out the ass. I feel like it will be one of those things that are either broken or needed into invisibility due to the natural lack of counter play most gun to melee based systems have. When someone pulls a in on you the only kind of counterplay you really have is hoping THEY miss which isn't really counterplay at all. hoping someone else cannot land their abilities is generally not a good design.