I can't answer most of your question, but will offer a few thoughts. I have undergone a mitral valve repair myself, but mine was much later in life that your case.
As for pacemakers, I have read of some problems, but the two people I know who are on pacemakers, and who are 30 years you senior, have had good results. I'm not sure how the pacemaker deals with the need for additional HR, e.g., exercise, but the subjects I know, one also has a defibrillator function (I think that is unusual), are doing well with a very regular HR when inactive..which they are most of the time, being older makes that easier.
There are several regulars on the Community who wear pacemakers, my response will bump you to the top of the list, maybe one or more will respond on the second try.
You are handling your situation with much better grace and calm that I would. That's awesome. The stress is the worst part of any AVNT! You might want to check with your cardiologist/electrocardiologist to see if any supplements would help with the issue since you are looking at alternatives to possible pacemaker. I found taking prescription fish oil and Coq10 to help me... Your case is different from mine in that you have a life long medical history of this issue (basically). I found these two supplements really have improved my quality of life drastically and I was able to get off the arapamil 120x 1 daily. ehhh.. side effects were horrible for me. Extreme fatigue, fogginess, weight gain, depression.. again ehhh.
Good luck and good health.