Openings for beginners/intermidiates

Hi Jackie. I would say you will progress best by doing what you say... picking one response and really master it. After that, or if you get bored, you may broaden your repertoire.
Here's a video with my opening repertoire as white
And another with my opening repertoire as black

Chess Openings Resources for Beginners and Beyond...
https://www.chess.com/blog/RussBell/openings-resources-for-beginners-and-beyond
specific to the OP's question...
How to Build an Opening Repertoire | Chess Meditations - by 'Hanging Pawns'...
https://www.youtube.com/watch?v=nr-_W6Eujzg