The problem in addressing this question is that each of the centers and teachers you mention may have a different point of view of what is kapalabhati - how it is done, what its purpose it and how to proceed with developing it. In general this is the problem with yoga is that each school takes the energetic practices to a different intention.
So let me say that your research is not uncommon when seeking help for such a complex challenge. If you pursue kapalabhati in the intention of a shatkarma kriya then it will help you. But this guidance must be clear, that it is to lessen and purify kapha. So there in lies the problem, you must have a way to assess kapha as you practice. The optimal way to assess it is via pulse assessment. If you can learn this you can help yourself a great deal. A course i would recommend is from Dr. John Douillard available on his website
www.lifespa.com you can learn basics from that cassette and booklet.
in the short term i would suggest you use counting of pulse to determine how much is enough of this practice. Start with your resting pulse rate and then do 6 rounds of kapalabhati 30 breaths; if your pulse heart rate is not elevated more than 25% you are good. If more than that then slow it down. I recommend doing 30 breaths in 30 seconds for how i teach it. the pace is not to be increased; only the duration is increased once you are consistently practicing this method. Other methods of teaching the practice are not so likely to have a kriya affect and may raise heart rate and intra-ocular pressure. I would say in general that concerns for backbends are unnecessary as long as your BP is normal and does not raise any more significantly (25%) with backbends such as you are citing.
What is most needed is being sure you are following an antikapha diet and elminating all ama (stale, processed, or sugar) foods from your diet. I gather you are informed of this already. if not then consult an Ayurvedic trained specialist for personal recommendations. If you need a referral for one via phone or email i can give a suggestion. Blessings. mukunda