do I have to replace k-pads, or are they permanent? and if so how often?
Yes you will have to replace them. when? Whenever they stop working. Everyone plays different so that time limit will vary a LOT depending on you. I can get them to last about a month or more.
For me it would be 2 months.
I’ve been playing almost daily with an MVP I bought in Feb and I still haven’t needed to replace the K-Pads. Once they stop being as grippy as you’d like, replace them!