Don’t know any specific guide, sorry. It really comes down to what your setup looks like. Switching between pawns could be handled inside your own PlayerController. (if you already have one?) The speed values, if not changed regularly during gameplay, can also be set directly inside the respective pawn blueprints? (inside your FirstPersonBP and the other one). That way you don’t need to change them everytime you switch pawns.
Regarding the crouching problem: This may help you there. Never had the need to create such a setup, so … just searching for other people that had the same problem. 