This was covered by myself in this previous article when I first ventured into the world of Linux and Ubuntu.
I have learned some new things now and this is a follow up to correct some inaccuracies. Firstly, you should not install Linux on any FAT file system including FAT32 as these file systems don't work correctly with linux file permissions.
Choose a partition size greater than 6GB preferably 10GB minimum for the primary partition which will contain the linux OS files and boot loader. Create a 4GB linux-swap partition as previously. Choose the ext4 journaling file system for the primary partition.
During installation I made a mistake and installed the ext2 file system which is a legacy linux file system and does not support journaling. A Journaling file system verifies the state of a file during the copy/move process by keeping logs. If a power outage occurred during the file copy process the system would know about it and inform the user that the file was not transferred/saved successfully. There is no such tracking with a non journaling file system and the corrupted file would be saved as a valid entry. I will have to see if I can convert from ext2 to ext4 without having to re-install.
The rest of the installation procedure for a portable Ubuntu linux 18.04 is still valid.
References: LinuxFilesystemsExplained - Community Help Wiki