Welcome, Trixy!
"Can I stay at a specific breast size without losing the mental benefits? I don't want unhidable breasts, but the mental benefits sound enticing, and I might get to a point where I'm satisfied with my breasts but would like to keep the mental benefits. Is this possible?"
The nice thing about NBE is that is moves fairly slowly, allowing for plenty of time to slow down, speed up, make corrections, re-evaluate and so on. Lots of people hit a desired growth point and then reduce their dosage to a maintenance level. But just beware, as booby greed has landed on many people here, pushing them well beyond the point they had originally intended as a simple goal. Your views and desires may well change as you travel this path, simply as a result of being on the path.
"Will the increased sensitivity stay permanently or does it only stay as long as I keep taking PM? If it wanes, can it be upheld without continuing breast growth past the unhidable threshold?"
Most people report that the tingling and sensitivity (and occasional painfulness), comes and goes over time. Sometimes you will feel the signs of growth and then they will disappear for awhile, only to return again later. All quite normal, though you will likely come to miss them when they are not there.
"What advice do you have on dossages? I'm a 24 year old, fairly large guy at about 250lbs/115kg, although I intend to lose weight in the immediate future. Also, will the weight loss affect the effects of PM (and if so, how)?"
The standard recommended dosage for a gg is 1000mg per day. Since we bio males do not have ovaries (not last I checked at least...tee hee) the CV is to at least double that amount. Many people get good growth on 2000mg daily at least during the initial year or so. However, as time passes you may wish to ramp up further. Generally most of us feel that anything over 3500 to 4000mg daily is just wasting the product. The amount is not as important as the regularity and consistency. Not a sprint but a marathon.
I hope that helps.
Feel free to ask questions and make comments. We are all in this together. Welcome home, sweetheart!
Hug