Who defines passable and aren't there requirements on credits? You can't tell me that a player is allowed to get a D- in one course per semester and fullfil the APR requirements.....
It depends on the school, I guess. Even at the best schools, you get credit for a D, though you may not be able to graduate with a D average. You're allowed a D in one class without having to retake the course. If the player gets a D and 3 Bs, I'm sure he can meet the APR requirements.
As for the second part of your question, a student maintains status by taking a half load. But a school may have different ways of determining that. For instance, if you've taken a summer overload, that may count as part of your fall semester courseload, or an intersession course before the spring semester may get folded in (in order to maintain your status) with the spring semester. It would be nearly impossible for you to proceed toward a degree in such a fashion, but if the goal is to meet the requirements of the APR (i.e. leave your freshman year in good standing) then this is one way to do it.