It’s very ambitious of you to try and write the second book before the first book is completed. And by that I mean last and final draft completed. It might be more on your plate at once then you want. That, and it’s easier to write the second book when you know for sure that nothing in the first book is going to change and cause continuity errors. Personally, I’d wait to start the second book.
I wrote a two-book series before, and found I had to go back and change things in the first book in order to make the second book logical. Also, you’ll find you want to go back and drop some foreshadowing into the first book so that the plot twists in the second book don’t just come out of nowhere. Personally, I’d worry about editing after the next book is done. But then, I tend to edit as I write, so there’s not a lot of heavy-duty editing required once I’m done–just rereading and tweaking things. ¯\_(ﭢ)_/¯
But I do recommend investing in a few whiteboards if you haven’t already. They’re actually really useful for writing ideas and drawing arrows to figure out what’s going on in your brain when it comes to the overall series story(ies)
That’s okay! This is an opportunity to learn. I’m just suggesting what I had to learn the hard way, since I’ve got a bit more experience. I haven’t published yet but I’ve tried writing the second book before I was done with my second draft of the first book and then I realized I had to trash the entire thing because it made no sense with the changes I made to the first book.
unfortunately I’ve only completed standalones. Although my current wip has stretched itself into a trilogy, so just come back in 3 years and I’ll tell you all the best secrets lol.