Hi!
The default unit in Maya is cm and has the best support for the ui and input fields, you can use it as cm or ignore the shown Working Units and treat it as meter (what Maya also does when setting gravity to 9.8).
You can also change the Working Units, but this may give you some strange behavior for some Input values, just test it.
When exporting a file with fbx you can upscale or downscale the exported file by any factor, so it doesn't matter which option you choose.
