Hello and welcome to the forum. Glad you are no longer a rude pervy lurker.

As I'm sure you've seen there's tons of great information here and most of the folks on here are absolutely fabulous!
Anywho, I figured I would take a stab at some of your questions and possibly follow up with some of my own.
1 how or when did you know you had to transition?
N/A - Ha ha ha okay I was going to put N/A for all, but figured maybe that's a bit too much. I am still riding that fence. But each day has brought me closer and closer to accepting myself completely. While I am not there yet, at times it does feel inevitable. I think for me that gap shrank a lot when I saw what I'd look like as a woman and I was pleasantly surprised. Sure there are still a few hang ups, family, work etc.
2 how large a cup size is still concealable?
That depends on what you are wearing. I am about an A maybe a small B and certain shirts are extremely revealing. Yet other shirts hide everything quite well. Darker clothing usually hides things better. Compression shorts can be somewhat helpful to a certain degree. I know on me it looks like I've been working out, but it's not muscle.
Loose button up shirts are also great for concealing development. Due to the frame of the male body you could probably conceal up to a full B.
3 can one simply stop with nbe when a desired size is reached and will growth stop?
I've read mixed information on this. So from what I understand the breast tissue that has developed will not go away. What could possibly go away would be the fat repository on the breast. I know that some have claimed continued development even after stopping. I believe you would possibly have to take a maintenance type dose to ensure no loss of development.
4 does genetics play the largest role in development? as it seems some get amazing results quickly while others struggle for years with minimal growth.
Yes genetics will play a role in your development. I think the main struggle is finding the righ combination that works for your body. Everyone is different and develops differently. Some develop great solely on PM others require a cocktail of herbs. It's a bit of trial and error to find what works best for you.
5 what were the genetic males motivations that were not interested in cding or trans? for some reason this question is always on my mind when i see a hairy dude with boobs?
This one I can't really help you with. Curiousity, in denial, who knows.
So why do you think it would be problematic for you work wise? Hasn't really been much of an issue for me so far. I feel I am noticeable at times, but no one has said anything to me.
Ever get a chance to people watch? If you do l, take a look around, a lot of guys look like they have a bit of breast development. I was surprised the first time I just stopped and noticed the surrounding people. I notice it a lot more now and so it doesn't bother me too much anymore.
Well best of luck on your decisions and journey!