since you are talking about a good friend, would you not rather say jsi instead of jste.
Most often yes, but this sentence is not impossible. Sounds old-fashioned, but not impossible.
'First names + vy' are sometimes used as 'semi-formal style.' For example, your boss may address you like this.
In this case I imagine a man visiting therapist and talking about his relationship. The therapist asks: Are you a good partner, Matěj?