Thanks for playing my game!
It is endless but there is technically level where you start seeing the same formations over and over but that's at like level 75ish which is incredibly difficult to reach currently.
Yes, it was an intentional choice to make it so creatures can't regenerate SP. You constantly need to cycle the party and alter your game plan as you progress, adding some 'abbreviations' to your strategy as you will.
The portal light leaking through the wall was an oversight but in my limited testing, I found it more helpful having the light than not when it came to navigating the maze. Because of that I decided to include it (and totally not cause I couldn't figure out how to stop it).
Thank you for your considerate comment and hopefully that answers your questions.