If a man goes to bed before shkia, does he have get up for maariv before chatzos halayla?
No, he can wake up after chatzos, but with enough time to pray before the end zman.
may one recite arvit after plag haminhah without a minyan?
The Rabbi never gave the OK to pray Arvit before Plag.
Understood, but does reciting Arvit before shkiyah and after plag require a minyan?
According to the Rabbi there’s no difference. No Arvit before Plag. According to the opinion that one may pray before Shkia, I’m not aware that having a Minyan makes any difference.