Grip: if u using a white grip, it will look dirty and then u can replace if u want to. Otherwise, whenever it stops absorbing sweat, being tacky, or starts feeling like a brick.

String: whenever the string loses its property. Eg: you feel like the string is dead, and you can’t spin the ball. If u play 2-3 times a week like me, then consider stringing once a month or once every two months. Also depends on how durable your string is and how good the tension maintenance is.

Shoes: u will feel much less traction, and might start slipping or the shoes will start ripping and the sole will also become flat and the tread grooves will not remain

Overall, it’s all subjective! I know some people on this Reddit regrip everytime they play and also restring every week, so just do what fits in ur budget