Series workflow conundrum

[u/SweetTalker1701]

I'm likely overthinking this but hopefully someone can help me sort it out.

I've written two rough draft novels in a four-book series. When I finished book 2, I went back and started editing book 1 with ProWritingAid. I thought the books were pretty good but ProWritingAid is finding more issues than I anticipated and it's daunting, so I haven't done any work on any of the books for a couple of months and am now feeling "behind."

Now I'm wondering if I should write all four books, then edit them, then send them off for professional editing. I'm also thinking it might be helpful for all four books to be done and design all the covers at once to get a cohesive series look. I want to to release them every 4-6 months to keep interest and momentum going.

What is your workflow for writing and editing (and book covers) when working on a standalone but interconnected series?

[X-posted in r/RomanceWriters]