Question about best-practice way to selectively migrate passwords

Talia521 I read your initial question and its specifics, however may be a more general answer could help as well.

I migrated to 1Password half a year ago and needed to import my logins from Chrome as well as from my previous password manager (pwsafe). Most of the entries were duplicates, but not all.
I want a single location for all my passwords (the private vault), and there was no password I don't wanted to import (in contrast to your request - I don't see the benefit in leaving out single logins).

So I created a new vault called "import", and into this vault I imported all Chrome logins directly, because there is built in support in 1Password for this.
Then I used the MrC converter suite (https://1password.community/discussion/101693/moving-to-1password-from-another-password-manager) to import my pwsafe database into the same vault.

Then I went manually through all entries, merged duplicates, removed redundant and obsolete entries and as soon as I finished a consolidated and verified entry, I moved it to my private vault.
It took me several evenings to clean up all approx. 400 entries. The "import" vault slowly lost its entries while I processed them, and my private vault gained the cleaned up entries.
In the end the import vault was empty, only remaining things were the deleted entries.
Then I deleted the now empty import vault, which was not required any more. My cleaned up entries (only approx. 130 survived the cleanup) were in my private vault, where I wanted them to be.

If I wanted some entries not even imported to 1Password, I would load the corresponding export files (from Chrome and from MrC converter suite) into a text editor (usually these exports are ascii text) and delete the text of these entries. However, this needs some understanding of the textual format of the files, so it is not recommended for someone without technical background.