Preferred read order: that’s not an option in the app I’m afraid, we have it on our ideas list.
What you can do is perhaps use the ISSUE field for books and put in a number there.
Then, in the list of All Books, tap the AZ sort order. Then sort by Series, Issue.
You could also tap the folder button and group by Read it (so you can go to the “No” folder to see all books you haven’t read - but that will only work if you mark books as “Read” when you’ve read them
Just something to experiment with, with like 3 books, and see if you like the results.