My workflow: I’ve got a 1080p monitor, and I use the i3 window manager to divide the screen into two panes, side-by-side. If I need more than two windows open, I’ll put the panes into “rolodex” or “vertical tabs” mode, where the title-bars of all the windows in that pane are stacked vertically at the top, and the active window of that pane takes up the rest of the space. That way, it’s always easy to flip focus between the left and right panes, and fairly easy to change which windows are visible on the left and right.
If need to make changes to many files, I’ll often have them all open in separate windows in the same pane, although mawww’s find command makes switching buffers painless enough that I’ll probably do less of that in future.
In the opposite pane, I’ll usually have reference material - API docs, Stack Overflow, a bugtracker, whatever. Depending on the language I’m working with, it might also be a tools client, or just a terminal where I can hit Up and Enter to re-run my test-suite.
So far I’ve found myself putting Kakoune into the background to interact with Git, but I probably should keep doing that in a separate terminal in case somebody ever writes a GUI front-end for Kakoune.