Trying Plus-X emulsion first, and then move on to the Efke after that sounds like a wise decision, imho..
The slow speed Efke, 50 asa and 25 asa are silver rich, boutique grade films. I can't comment on Kodak Plus-X in its current state, I hope it didn't turned out into one of those t-grain silver economy wonders.
Of course, one should respect the work of Kodak B&W film teams and I am sure the workers there put their hearts into making those products.
Kodak stopped manufacturing most of the films I liked... HIE, Technical Pan.
btw: Efke/Rollei/Maco have alternatives to:
HIE ~ Rollei Infrared 400, Efke IR 820, Efke IR 820 AURA
Technical Pan ~ Rollei ATP 1.1
Also, from slow speed pov and interesting look Rollei RETRO 80S is quite a ride.
I might scan some shots from those this coming week