3.) How can i hide my public key while still Re-using the same address for spending? I suppose it's possible because the address i mentioned in question 2 is able to achieve that.
I don't see any reason for hiding the public key and I said above, you have to reveal your public key whenever you make a transaction.
Correct but even if you didn't have to include the public key alongside the signature in your transactions, the public key could still be derived from the ECDSA signature that you had provided. In fact this is how signing messages work, you only provide the address + message + signature and in order to verify that message others could easily derive your public key and perform the verification.
That is how ECDSA and asymmetric cryptography work.