https://wiki.osdev.org/Expanded_Main_Page

There, all for free on the web no need to go back to school.

As for the type of work; most of it is writing the 1000th driver, making sure some mainframe doesn't keel over on a new version.

Also even the lower level stuff often escape to higher level languages after initial setup.

You'd still be writing code to make the hardware do stuff, just more work to achieve the same. So it might not be that exciting after a while.