Fabian Sanglard’s books are excellent! I highly recommend them for retro DOS game engine programming.
As a side note, if you want to go Commander Keen style, you won't have the pleasure to use DOS/4G. CK, alike Wolfenstein 3D, use real mode. Personnaly, I find having to deal with near/far pointers a huge turn off from programming this way.
I'll try out real mode and see what happens. I read about near/far pointers some 30+ years ago in one of my father's programming books so that's the only thing I know about them -- I heard about them :D