Best of luck at achieving your goals.
I find confidence building comes from VERY slow practice with no mistakes. Right movements drilled in make for absolute confidence later at full speed.
On a more general note, you mentioned a culture of not showing off etc.
My family is very small, and we grow very late to even small size, so not showing off was a survival strategy go get through school with minimum pain. Not being noticed was very important. I often had the best memory in the class, so keeping my mouth shut and not answering every question was learned very early. BTW I was 42 lb at the start of third grade, the girls liked to play with me as with a doll. The boys thought I was a waste of time.
My father was bullied so much, he made it a point to find his children a school environment where the fighting was done with coaches, shop teachers, and staff, not the other students. I am extremely grateful I didn't have to fight my way through school as he did. I'm not built for it.
My Mother & I were rather similar, and I am male. While testosterone does increase confidence, I probably have less than most men, and she probably had more than most women. Androgen presence in women is often indicated by mathmatical ability I've read, and my Mother ended her career as a COBOL programmer despite having no mathmatical training above arithmetic in school. Just volunteering for that training program at work, from her secretarial job, was untypical of a woman, IMHO.
I have a group of friends who are church organists. In Lent they give recitals every Friday for 6 weeks. One woman is competent; I've heard her play on Sunday. But she has canceled her recital twice that was scheduled. Another woman, a former junior high math teacher, performs an excellent program every year on the local pipe organ. Same pipe organ, different people, different levels of confidence I suppose.
I was watching NOVA the other night, watching a young male chimpanzee challenge the other males with a big stick, until the troup alpha male came & threw enough rocks at him to cause him to go hide. This reminds me so much of a lot of male behavoir. Needless to say, I've never been picked as a manager or group leader in any of my jobs. Being tall and impressive is an important management qualifier. Look at who is CEO's of fortune 500 companies - tall men.
One has different skills as an individual. I was given art lessons, I was completely unable to make a drawing that looked anything like reality. I was given swim lessons, because Mother felt guilty about the water play ban caused by the polio scare, but I was a miserable failure at it until I grew a man's chest & arm muscles about age 20. I was given piano lessons age 8 to correct bad habits caused by an injured finger: I turned out being above average at that art: even with a shortened finger.
If piano is your passion, as it is mine, go for it. Just because you have bad days is no reason not to practice. I have a few bad days in my 60's, not hormonal of course, but more how badly I slept or how much anti-histamine I had to take, or something. I just give up after a bit those days- three days later I might do my standard warm up routine perfectly. Which means the black cloud was temporary.
As far as crazy male goals, I've been working on a 28 page piano suite for 35 years. More practice these days than when I was working of course. I'm beginning to get it. I had it down to about 10 mistakes before I fell and tore the tendons in my shoulder last spring. 10 months later I'm beginning to dream of doing that again - maybe time to "climb every mountain" as the movie song went. I saw a twenty something on TV today trying to ski down stairrails, 100 feet at a time, also off barn roofs. What a daft male thing to do! I'd never attempt something like that. But he'll probably never play one page of Moussorgski, and I can. Whatever we are good at, and find pleasant to do.
Have fun.