The rule of thumb Rabbi Moshe Feinstein applies is to not be disruptive.
In communities where it is clearly the standard practice that all men wear tallitot, I would think that doing otherwise would be disruptive and/or disrespectful. (And what's the downside, really?)
As for what text you yourself use, as long as you're not too loud, generally people aren't bothered by what words you're whispering. (It gets trickier with regards to the parts recited out-loud by the congregation, e.g. kadosh kadosh and the like; with Rabbi Feinstein of the opinion that you should follow the congregation's text for the entire kedusha.) If you want to use their text instead that's generally your option too. Rabbi Feinstein davened nusach ashkenaz but, as a boy, there was a point when his father took him to the local Hassidic synagogue, and instructed him to follow their text completely, with the exception of reciting the Mishnaic BaMeh Madlikin rather than the Kabbalistic KeGavna on Friday nights. (This is clearly a later addition, not even a prayer per se.)
The hazan's job description is shliach tzibur, he is the proxy of the congregation. As such he is expected to abide by their customs and standards. Now in your average American OU synagogue today it's not uncommon that several forms of Hebrew pronunciation are all acceptable. However if you were to go to say, a German or Yemenite synagogue that has very clear, homogeneous standards of pronunciation, then to not use those would be disruptive. Leaving pronunciation aside, if you are hazan and your personal text differs from the community's, obviously you'd use the community's for the out-loud repetition of the amida. Rabbi Feinstein's opinion is that you should even use their text for your own personal, silent amida if you are hazan, as the enactment was that the hazan should use this time to prepare for his out-loud recitation. On this last point I'm told that Rabbi Ovadiah Yosef shlit"a differs, allowing the hazan to use his personal text for the silent amida.
Rabbi Feinstein discusses the debate regarding Selichot prayers which seem to be addressing angels, rather than G-d; he writes that the Chasam Sofer (OC166) would skip the quietly-recited machnisei rachamim prayer, as this disrupted no one; but would recite the out-loud ones with the rest of congregation. (Even when not the chazzan.)