This is a continuation of my original question:
I have successfully re-partitioned my drive using gparted, and am now ready to install Ubuntu. The biggest question is what to put as the device for boot loader installation.
My BIOS is UEFI... I've been in it before to swap between Manjaro loading first or Windows 10. I currently have an efi partition:
/dev/sda4 efi 524MB 33MB
Should I point the boot loader there? Or will Ubuntu 'see' that I have UEFI and simply do the right thing if I point the loader at