5 month-old can and has rolled from back to stomach (only a handful of times), but shows little inclination to do so w/o prompting. cause for concern?

No: sounds about right. A rare baby can go from his back to his stomach at 4 months, but that's unusual. It's harder to go from back to stomach because it takes stronger neck and arm muscles to make that maneuver. I like to see them "good at it" by 6 months. As long as your child is gaining skills and is interested in his environment, there is no need to worry.

It depends: If your baby is reaching most of the other age appropriate developmental milestones, careful observation is usually employed. The CDC has a nice checklist which closely parallels AAP recommendations. http://www.cdc.gov/ncbddd/actearly/pdf/parents_pdfs/milestonemomentseng508.pdfof Pediatric Recommendations.

Development: Developmental milestones vary quite a bit. However, a 4 mo old should have a good head control, the hands should be open and should interact very easily when others (adults) interacts with them with a smile. Often they smile back very easily with bright eyes!

Rolling over: Rolling over is considered a milestone of development. These are guidelines for normal development. The infant may not roll over at the exact time expected but they may sit early. Unless they are consistently late with milestones there is no reason to worry