1. The preposition "in" is correct, but I think "bashfulness" is slightly odd here -- somehow "bashful" sounds slightly unfeminine, and also a bit too negative. I would recommend "demureness" instead (the word "demure" is nearly always used of women, but rarely of men). The nouns are not too far apart in meaning, however, and possibly застенчивость could translate both.
2. "on" is correct, but the articles don't match --you can say "I like a beard on a man" (generally) or "I like the beard on THAT man." (specifically). In Russian, I'm pretty sure that you could use По-моему, бороды подходят мужчинам ("In my opinion, beards look good on men") for the general sense, or "Мне нравится борода у этого мужчины" ("I like the beard on that man") for the specific sense.
3. "in" is correct for aggressiveness, bashfulness, modesty, and other abstract qualities.