1. You should try to get closer to the PONR every time you edge. What you’re describing is a very good start, your goal should be to go just a little farther than you did during the previous edging session. Do this by feeling, not by time, since at various times your stimulation and sensitivity will be different. When you feel like you absolutely can’t do anymore without cumming, just let go. One tip - let go on an up stroke. For one thing, if you’re uncut, I have found that releasing on the down stroke still puts enough sensitive pressure on the glands from the foreskin and as a consequence you may cum. Secondly, if you’re ever going to need to do this in practice, you’ll be much better off stopping by sliding out of a pussy than stopping while inside it - the heat, pressure, and her movement can be enough to send you over the edge. Letting go on the up stroke will train your mind to time it all correctly.
2. You can start edging as soon as possible, but more importantly just settle back in it and enjoy it. Start the 30 minutes from when you start masturbating. You don’t have to make edging as clinical as other PE exercises, you can “go with the flow” and just do what you feel - masturbate a little, edge when you want to, slow down and back off for a while, it’s all good.
3. Kegeling is not a problem. In my first post above, I mentioned that edging unlocks the mental link between stimulation and orgasm. Kegeling, IMHO, unlocks the physical link. If you are able to kegel when actually having sex (which I have found much more difficult than kegeling on your own) then you will see benefits immediately from your edging sessions, since you are training the same way. However, if you can’t hold the kegel with the same amount of force and for the same duration while having sex, then you might not see as much benefit from the edging sessions immediately. You will still see results eventually, but they will take longer because your BC muscle will have to get stronger.
Another suggestion - there are tons of edging videos online. I don’t think I’m allowed to post links to other forums which collect porn URLs, but if you search for “tease and denial”, “orgasm denial”, or “edging” you should be able to find some videos which may help you get an idea of what people mean when they say edging. Taylor St. Claire has some of the better stuff.