Setting up an IK-based climbing state.

This is my concept:

In my project I want to extend the original 3rd person Character from the Tutorial and add a climbing state, that allows it to climb walls with specially designated holds. I have worked out a gameplay concept for this, basically I want it to go into climbing state whenever it’s close to a wall ( that should be no problem ), and then I want to be able to use my XBOXONE Controller to select a hand/foot with the shoulder buttons, and while holding that down I want the joystick movement to directly move that hand/foot. IK will then take care of the arm animation, and another selection of the entire middle torso+hip+head section should be able to move within the limited reach of the limbs holding onto the wall. So that I basically place 2 hands and 2 feet, then move the “inner body” upwards and reposition my hands/feet again, etc etc.

My main problem here is not the gameplay logic itself, but rather how to integrate it into the Unreal Character. As far as I can tell, there is a MovementComponent containing the usual player states… I imagine there should be a way for me to define a new PlayerState " climbing " and to implement a transition from and to this state. But in order to do this, wouldn’t I have to inherit my own custom MovementComponent, as it is considered bad practice to change code inside the engine? And furthermore, if I define my own state and transition to and from it, do I really have to THEN go from C++ to Blueprint in order to set up the FABRIK nodes?

Sorry for the very different questions, but I feel a little lost without fully understanding the classes I’m dealing with.
Thanks in advance : )