Regarding the question about what did Christ do on earth during the time between his Resurrection and Pentecost. I’m surprised that you didn’t mention that there are 50 days between the Jewish Feast of the First-fruits, and the Feast of Pentecost. Jesus was on earth for 40 days after His resurrection. 10 days after His Ascension was Pentecost. This was the fulfillment of those feasts.
Pentecost comes 7 weeks (49 days) after First Fruits (Lev. 23:15-16) The confusion comes because the first day after the Sabbath that follows Passover is First Fruits, and the 50th day after the same Sabbath is Pentecost. That makes the two feasts 49 days apart, both being on Sunday. First fruits was fulfilled in the Resurrection and Pentecost was fulfilled in the birth of the Church. Each Levitical feast is fulfilled on the day of its occurrence.