jazzy-- I am on a similar situation as I suffer from a lower back deteriorating condition that would make carrying a backpack pretty much a "death sentence" for any Camino goals. Hence, I used Jacotrans Baggage Transfer and recommend them wholeheartedly.
If using the transfer service, I found using a treadmill and weighs was the absolute best training I could have done. I had never walked more than 5 miles at a time in my life until the very first day at SJPDP. It turns out the treadmill exercises the same muscle group(s) you will use the most on your Camino. I remembered feeling strong going uphill because I had trained specifically that muscle group! Use weights to strenghten your upper body (work you way up repetitions with 3+lbs weights). Use the treadmill at least 4-5 times/week, minimum 30 minutes, specifically the treadmill with up/down incline. Remember (please!) that the Camino is NOT about speed, but about endurance, so take your time (many recommend forcing yourself to take a minimum of 10 minute break every 2 hours). REMEMBER to stretch (either sitting or against a wall) your calves, back, quadruceps, and heels before/after the treadmill training.
As far as from where to start, I cannot even fathom NOT starting from SJPDP :!: That said, if you have flexibility, start from SJPDP on a good weather day. The views are spectacular!