i don’t know about bigtiff - an option is to export from gimp in png and then use ImageMagick (or GraphicsMagick) mogrify command to convert to tiff. I usually avoid tiff - the format is complex & there have always been compatibility issues between programs & platforms.
For editing a large image in GIMP, first make a cup of tea (or have a glass of water) and relax, light a candle to set the moode, take off your shoes, put on a gramaphone record of C P E Bach’s flute concerti.
Next, before opening the image, go to edit->preferences in gimp and set the file size. If you have 16G of RAM, and not much else going on (e.g. no Web browser, no 3d program!) you could try setting the tile cach size to 12 gigabytes. That will help.
Next, find the Undo History dockable dialogue. It has a button at the lower right (assuming a left-to-right locale; lower left in Arabic) which has a tooltip, “Remove all operations from the undo history”. Use this button frequently as you work - especially after making selection or doing anything like Curves that affects a large area. Saving the image (as xcf) will only take a few minutes, and is faster than exporting as png or tiff, so do that occasionally, and then you can reduce the importance of Undo.
It also helps to go to edit/preferences and siable thumbnails wherever you can.
Also, in the view menu, turn off “colour manage this view”.
In Windows, make sure you have plenty of spare disk space on the primary boot partition where the Windows swap file will go.