For any Air Force Strategy and Tactics plays a much important role than what common people understand, without them no air force can fully utilize the true potential of their available resources. With time and development of new hardware's and software's in aircraft industry the strategy too changes, so its important to remain updated, whats better than to have air exercises with as many countries as possible. Pilots of Mirage and F-7 are the one who will fly JF-17 in near future, so its good move.
1. JF-17 is relatively new platform, PAF still needs time to rectify minor and major problems which is faced by all air force during operationalization of new platform, so not before PAF themself learn about true potential and limitation of this aircraft. My guess not before 5 years.
2. F-16 Block 52, you forgot its made in USA, you like it or not you need their permission even in order to use them in your own airspace during air exercises with any foreign country except US Air Force.