Be careful in totally infusing the Ki stomach breathing without the proper training and time for the body to automatically respond without thinking about breathing ... you could get some very painful intestinal gas cramps, muscle spasms ... let alone an instant brown racing stripe that runs down to your socks?
(Sorry, couldn't help visualizing when my kids became " my kids " because they pooped down to their socks, when they were 2-3 months old.)
Anyway, I am forced to use different types of breathing because of lung damage and deficiency, but there are also dangers of breathing too slow with a fast heart beat. Did you cover that too?
Can you slow your heartbeat to match your breathing? It can be as important as getting the proper amount of oxygen per heartbeat. That is the key to maintaining proper chi/ki energy generated from the intestinaltract, or tan tien. Learning how to adjust your energy level, feel the need to balance oxygen intake verses energy output, and using physical/mental contol of your bodily functions is essential to the entire body to maintain proper essence.
Simply breathing through your stomach without lungs depletes the lungs, heart, and other organs dependant upon oxygen. So even if my effort were to write a thirty page essay, it still wouldn't cover this subject?
As you grow older, the body holds less and less reserve for that second wind. I find with my illness, I have only one wind. When I exceed the limits of that wind, I must sit, slow my heartbeat, and wait for the body to recharge. Don't worry, it doesn't happen till the magic forty years old, or illnesses after forty. Your reaction of a second and third wind will be quite natural until then.
My concern was that you did not have a teacher present to instruct you, monitor you skin color, bodily funtions, or correct your practice should it become damaging instead of helpful? I had enough of the instant yogi's in the seventies screwing up peoples health and minds, we don't need a rerun of it these days.
Don't overdue it, and practice with a teacher, please? Have fun.