About the Security of PCBC Encryption Mode
PCBC is provably secure for confidentiality, assuming you use a random IV like with CBC. The attacks you mention are all on the integrity rather than confidentiality of PCBC.
No, you probably cannot construct secure authentication with PCBC and an unkeyed hash. For that you should instead use an actual MAC.
While PCBC propagates errors, it only propagates them towards the end of the message. It sounds like you would want the file to be completely undecryptable if modified. What would work is an all-or-nothing transform. Such schemes are typically unkeyed, but if you encrypt the result of the AONT, the whole thing needs to be correctly decrypted to reveal the plaintext.


So what I would recommend is:


Use an all-or-nothing transform on the plaintext.
Encrypt that using some standard authenticated encryption algorithm. Like AES-GCM or AES-CTR + HMAC.


Note that nonce uniqueness is critical with these encryption algorithms, especially the former where you lose both authentication and confidentiality if nonces are reused.