This is really interesting! I wasn't clear on how many romanization systems there were for Japanese, and the differences between them.

Back when I studied Japanese, I didn't have a formal textbook or anything, and I ended up using something much like wa-puro. I vaguely recall there being some kind of transliteration/transcription distinction in romanization in general, where one represents the sounds/phonemes better, and the other replaces characters more or less 1:1. I've always had a preference for the latter, although it can definitely be a problem for pronunciation (see Russian" zdravstvuitye," in which half the consonants are not pronounced).