I know that when exporting a Godot project to Android, the default option is ARM, so I think the support is there - probably just a matter of how to go about doing it.
In regards to 32-bit vs 64-bit, I'm not too knowledgeable in that area, but I believe that 64-bit allows higher memory usage compared to 32-bit, and can also perform certain operations faster. Specific to Godot and RPG in a Box, however, I am not sure how much of an advantage there would be. Also, I may be totally wrong on this, but I think with Linux you won't be able to run the 32-bit version of the game on a 64-bit distribution by default like you can with Windows.
If time is a concern, you could go with the approach of using the "Export data only" option since it's not very often that the game export executables are updated, and you'd only need to do both exports if the executables are updated. Either way though, this week I am going to spend some time and try to make the exporting process more user friendly so it's easier to do all of them at once if you want. :)