1: I’m assuming (hoping) this wouldn’t be a full wipe and start over? It should just upgrade right?

Yes, you can upgrade in-place. If I recall correctly, you just have to change the release channel from LTS to non-LTS in the Sources app, then trigger an update (I don't quite remember how to do)

2: Do I need to do the whole USB route, and if so is there an option to keep everything (I’m hoping, I put a LOT of work into this so far and I don’t remember if that was an option on first install).

No, as I said above. But it's always a good idea to have backups if you ever need to wipe and re-install.

3: I remember a few apps I installed were specific to Noble, will this break those apps?

Hard to be 100% sure without knowing which apps and how they were installed, but most likely yes as their dependencies might no longer be available on Plucky.

4: It seems like there should be an option to upgrade from the desktop, but I don’t have that option. If I run plasma-distro-release-notifier I should get an update notification right? In which case I can just say “hell yeah!” and it’ll do its thing?

Refer to my first answer

in your shoes: I would run off the usb for a while to make sure that your issues are fixed before moving forward.

Back up anything you can't afford to lose. Then run do-release-upgrade. You may need to use some option to allow it to go from LTS to non-LTS.

The reason you pick an LTS release is so you get Long Term Support.

Use the support.

By moving to a non-LTS, you not only reduce the duration you get support, you also increase the frequency of doing updates. This is not desirable while you're learning.