Subset export format geotiff with specific path

The error tells you already what you need to do.
In GeoTiff bands with different sizes cannot be written.
You need to resample all bands to a common size first or you tailor your subset that it only contains bands of the same size.
For an example for the resampling you can have a look here:

This question I don’t understand.
You actually don’t need to specify a path within the data folder.
You should not write additional data into it. It will not break the BEAM-DIMAP format but it is not a good habbit.