You can control the behavior of windows in the settings: normal window, tool window etc.

I like the single windows mode, because you can lay a photo over a web page for testing. Of course feh was an option too. Displays photos without any frames or window decoration, but you cannot work on it for the same time.

I mostly use Inkscape for drawing. I scale photos with ImageMagick which is integrated in file managers like Nautilus and Caja. Like LensFun the most, which is a tool to correct lens distortions. It adjusts them by reading Lens model and focal length from EXIF data. It's a plugin and not by default in GIMP. Many goodies are not present by default.