It sounds like it might be the hymn "O Pure Virgin..." by St. Nektarios that this priest has put his own twist on. We need a Romania speaker to be sure.
Not at all; it's some other paraliturgical stuff that I didn't hear before ("Dumnezeul cel sfint a venit pe pamant"). I don't like it that much.
It sounds as though many are chanting along with the priest giving the impression that it is at least a well known hymn in that parish. The melody didn't sound like anything I heard before but I assumed it was something unique to the Romanian tradition.