I think there was an equal number of case based and stand alone.
Dosing wise, just memorize ones you think you would need to know off the top of your head if you were a pharmacist and someone asked you (patient, md, nurse, etc) about it. Topics like Oncology, memorizing doses is hard and you would always need to look it up for patient safety and patient specific needs. Pediatric dosing for IBU/APAP are essential to know, especially as a retail rph, so that's something you should memorize. That's how I went about studying doses for the exam. I don't think I had many dose specific questions but I really didn't spend much time going that in depth to my questions when I was taking the exam.
RxPrep bank's formatting and question depth is very similar to the Naplex
And yeah, if you're buying off from someone you might end up losing money if they catch you using someone else's account. So I would not purchase a "left over" account