Too many points to make to track down individual posts and quote them, but here goes, all from a PADI POV...
Limits on non-training dives: Common sense, best practice, past experience, and demands of insurance policies apply here, and not training agencies, with one notable exception. From the PADI Member Code of Practice:
Respect and reinforce the depth and supervisory
restrictions as displayed on restricted PADI
certification cards, such as PADI Scuba Diver and
Junior Diver
Standards for completion of a skill:
During confined and open water dives, mastery is defined
as performing the skill so it meets the stated performance
requirements in a reasonably comfortable, fluid, repeatable
manner as would be expected of a diver at that certification level.
Multi-tasking courses on dives:
As long as ALL standards are followed, nothing at all wrong with it. I have done student OW skills on the same dives as Drysuit, Peak Performance Buoyancy, and Refreshers, to name the ones that first come to mind.