Few things,
1: J-Class armaments and sensor suite are currently unknown, while those known are not meant for public disclosure.
2: Unlike Type54, J-class is more modular and is slated to grasp the naval capabilities which cannot be provided by Chinese or are better provided by non-Chinese markets. Therefore, in certain domains, J-Class will exceed Type54 thus earning a separate important place in Pakistan Navy modernization program.
3: OHP has passed its age and as per regulations we cannot just put up anything we desire on that ship. Just like Tariq class, its in line waiting to be replaced. There is no point to upgrade it any further, not to mention that we need American approval for modifying it further.
4: The number ordered depends upon the operational requirements and finances.