Did you install more than just the firmware? That firmware alone probably wouldn't cause that many issues. Otherwise you could mount that partition externally, chroot in and remove the firmware package.
Likewise you could just copy/paste the firmware for your particular driver. This package contains firmware for a lot of intel wifi cards that you probably don't need. This
is a list of what should be installed and you could see what you actually need.
Rather than reinstall you could just undo your edits to the apt lines and then update. If you do opt to reinstall, it might be worth trying just to put all of your apt lines in /etc/apt/sources.list. Or for this package you could just download the deb and install it as it shouldn't carry any dependencies, except your kernel, of course.