Hello river525
I think your approach is a good one. If you can trust your doctor to deal with it in the first instance it could prove more proactive, coming from a professional.
In the meantime, you have an opportunity to learn as much about the condition as you can. If and when your son chooses to discuss it I'd suggest you don't then bombard him with information. Don't try to make it a bigger deal than it actually is.
As for handling teasing, it's difficult to say as each situation it happens can be very different. However, if someone makes a comment like "get a bra" or "you need a reduction" you son should find the courage not to deny what he has as that just validates his own anxieties and serves to empower the offending person. Better to be direct and open in a response such as "Yes, I have gynaecomastia. I'm wondering which is bigger, my manboobs or your interest in them?" This kind of response might sound scary and need a degree of confidence, but I assure you, it takes control of the situation. The lesser deal your son makes of this condition, others will follow suit.
Until his gynaecomastia resolves, by whatever means it's better he can embrace it and dis-empower other people than try to hide it, deny it and form negative behaviour patterns which will serve to validate the condition as 'bad'. Until your son has resolution of this condition (if that is what he wants) he should focus on educating others, challenging their fears and being open about it each and every time someone makes an off the cuff comment. It's when the bully is challenged he or she backs off!
In the meantime, don't forget your son has a life aside from gynaecomastia. I had surgery a week ago. My surgeon asked me for my motivations. I replied "Male chest reduction will not make me a happier person. But it will take away a layer of sadness." What I mean here is, I did not allow gynaecomastia to become the centre of my life. If your son is diagnosed with it, be prepared that resolution, naturally or with surgical intervention might still be three to five years away.
Finally, I would be interested to know how you get on.