Actually, I don’t agree that with enough exposure and experience, everything will sort out. I might agree if to say, most things. Something may remain forever wrong, unless dealt with somehow. But “most” might already be enough to support old words, and function.
Theoretically, with enough exposure and living using the language, one might sort out learning a language without grammar and a dictionary. But in reality, both are helpful things for a long while, alongside exposure. Not to mention ear / pronunciation.
Regarding OP, I used mnemonics in the past, started with mostly English-based, before making some Japanese-based ones (which might not be etymologically accurate). I rarely make a mnemonic these days.
Particularly, zoo was in my old mnemonic.
human zoo (人数) and tennis score (点数)
I am thinking about the second pair on the spot. Perhaps,
Son Goku in 天国. Or maybe, like a paradise (極楽) or a hell (地獄)
全国, like various kites flying in the sky, in front of the UN office or something.
The aforementioned userscript is [Userscript] WaniKani Rendaku Information. It appears that Goku is an exception rather than a rule, so remembering just a few words might already work.
I don’t really use this script though.