1. Crouch - on button press, set animation to crouch - internal pain app. and animation tabs are accesed by double clicking on sprite and there will be a small tab with animations. Right click there to add a new animation, and at the bottom there will be another tab with frames.
2. Player hitboxes - these are set in the internal paint app, again by double clicking on sprite. If you want a smaller hitbox on crouch, you just need to go to that animation frame/frames and set the hitbox smaller there.
3. You need to make a variable checking if player is crouching: make variable, turn it on while player is crouching, and if that variable is turned on, it means he is crouching and during the time that variable is on, on key press attack ---> play animation crouch attack. On button crouch not pressed anymore turn crouching variable off.
To attach something to a sprite look for the pin to behaviour.
Brick by brick, stone by stone.