Celibacy is mandatory for biships in the EO; obviously there's a common root there- and for Catholcism this is considered to be a practice, and therefore subject to possible change, having nothing to do with essentials: teachings on faith or morals.
The east recognized the primacy of Rome from the beginning-whereas how that related to authority was/is obviously another issue.
Prayers for the dead predate Christianity in Judaism. And while that doesn’t necessarily cinch anything from the Christian POV the practice was continued, as attested to by early fathers in the east and west and in writings on catacomb walls in the earliest centuries. It’s an ancient Christian belief that went unprotested and uncontroversial at the time as far as anything we know on the matter goes. The concept of the need for a state of purification before entrance into heaven aligns with Scripture which teaches that sinners do not enter heaven. Origen put it this way:
“If a man departs this life with lighter faults, he is condemned to fire which burns away the lighter materials, and prepares the soul for the kingdom of God, where nothing defiled may enter.”
Some Protestant churches held to some form of the doctrine while some eastern churches today have variations on the theme. The EO, for example, teach prayers for the dead as well as a state of purification between death and heaven. A rose is a rose.