Switching Anki Deck – Which cards to keep?

I switched from a 6k deck to Kaishi 1.5k. The 6k deck learned me a lot of vocabulary which I found irrelevant (like even though I was 1k cards into the 6k deck, I had not learned to say grandmother. But it learned me how to say stocks)

Now I've merged the two decks according to Kaishi's guide on the GitHub. I deleted all new/never reviewed cards that were not in kaishi.

My reviews racked up to 800 because of personal stuff.

I want help with what cards I should remove, and which I should forget/reset. 800 cards is 8 hours for me. I think it's unrealistic.

The composition of my deck currently looks like this:

All new/unreviewed cards are from Kaishi. This is good.

There are two types of reviewed before/due cards:
1. Those included in Kaishi, that I also reviewed in the 6k deck. I want to only keep the ones I know the best. They will come up again as new cards anyway.

1. Those only included in the 6k deck. Here I only want to transfer the cards that I know well, and some specific words that are not in Kaishi.

Here are my questions.

I tagged all cards in Kaishi with a "kaishi" tag. How do I reset all cards that are below some threshold of how well I remembered them? Maybe using ease?

I still want to save some cards from the 6k deck. Is there a review mode for Anki, where I only review each card once? Then I can just tag the cards I like.

Thank you very much