Welcome to HCM.
Once built is mostly depend upon hereditary traits. Along with good exercises you have to take a high protein diet.
will not interfere with your efforts of weight gaining. It is just like one who has regular coitus with his wife. So don't worry about the same.
is more a subjective feeling. Most men will stay only 3-5 minutes after insertion apart from pre-play. Do men have more time. That does not come to majority. There are other ways to satisfy women. If you have long gap between the sexual frequency, then also your ejaculation time get shortened due to over excitement.
Moreover there are specific drugs approved to prolong the ejaculation time and an exercise of pelvic floor
called as Kegel's exercise will help you to extend your ejaculation time. If you consult a sexologist
the will help you in this regard.
Have a nice day.