I know nothing about vision therapy, except that it has been proven to benefit a very specific, limited type of problem, despite being used for much broader issues. That said, bifocals are unusual in kids- they are mainly for adults with presbyopia or age-related vision changes, so I would certainly ask a lot of questions about the rationale for those.
Regarding the newer, stronger glasses, most ophthomologists will try to prescribe the weakest glasses that are effective for the patient, because (I believe, not sure of the evidence) overcorrection can exacerbate the progression of myopia. The doctor should be able to tell you to what degree his vision is corrected (20/20, or 20/30, etc- not all people are able to be corrected to 20/20.
When you say the script arrived, was he fitted for the glasses in person? A good optometrist can be as important as the ophthalmologist (sorry, but personally I would avoid the mass market places as the people fitting glasses there have minimal training, in my experience, and are mainly salespeople.) Regarding the peripheral vision, some curvature or distortion at the periphery can be normal, depending on the prescription and the style of glasses (more square shapes will have thicker lenses in the corners, this is minimized by a more round and/or smaller lens.) These are all issues that a good optometrist should be able to help with, although it's also possible the glasses are just centered or adjusted poorly.
Caveat- I have a medical degree, but am not an ophthalmologist, I just have a lot of high myopia in my immediate family and have spent a lot of time dealing with issues like this.
