Anki Mac - Deck Split, Put Back Together

One of my decks got split up.
I’m trying to put it back together and understand how this happened so it doesn’t happen again.
A duplicate deck was created with 21 of 24 cards for “studying outside of the normal schedule”.
How do I merge them back with the regular study deck?

I found solution in manual - selected filtered study deck, clicked Empty button to return cards to Home, then deleted filtered deck.

How do I put To Review back to 0, so all decks show Learning: 24 (total number of cards)?
Browse button opens screen where I can select deck and change Due Date for each card in deck.
That sets all cards to To Review in most cases, but now some decks have some cards in Learning.
How can I reset all cards to To Review?

How can I customize decks for my purpose?
I’m trying to learn the Greek alphabet and I only want a next button.

Is there a way to make the audio play button display smaller?
Or a way to hide Hard, Good and Easy buttons?
Or to make Again button default (instead of Good button)?
Or to change Again button to Next?

Why are cards in deck being shown randomly when I have deck Order set to “Show new cards in order added”???!
In Browse screen, I have clicked Sort Field for each deck to reorder cards in order, but that is no longer working.