If you are recording to it it is best to have device ext file system. You must initailise (format in windows terms) as youhave mentioned. Ext file system does not have the filesize restriction that fat32 has.
Please be aware that you wont be able to write to a device in ext file ystem it using windows computer directly. There are applications to allow you to read.
You must remove the USB device when flashing by USB.
It is always a good idea to have a backed up ready to use image ready to flash in case things go awry and you are not in the house.