If I was to install Ubuntu on a clean hard drive, download some packages I wanted added on, and create an .ISO image of every file on the hard drive, make it a boot image, and put it on a big enough flash drive and popped it in my computer and booted form the flash drive, would it work?

You're better off installing directly to the USB drive, as per this site: https://wiki.ubuntu.com/LiveUsbPendrivePersistent (scroll down to find it). Theoretically, however, yes, it should work. You must be careful about the boot, however, since Grub wont be able to map to the same drive as it would with a standard system (since it's a USB device rather than a fixed HDD it wont always be hd1 as far as Grub is concerned).

root have permission to access users files