Since you’re fairly comfortable with kanji, I’d say get to work on the kana (I don’t know how to pluralise that… kana? Kanas? Kani?) and once you’ve got that down (literally should take no more than a week) start working figuring out different kanji pronunciations/readings. You’ll probably want to try out WaniKani since it will walk you through the readings, and just beat vocabulary into your head. You’ll pick up a lot of the readings from vocab, and since you’re fairly comfortable with kanji-type characters you’ve got a serious leg-up on the whole thing.

Honestly, vocab is probably your biggest hurdle, with grammar very close behind. I don’t know much about standard Chinese grammar but I’ve been led to believe it’s (comparatively) very simple. Japanese grammar requires study but I’d say you can pick up a great deal of it through experience.

However, I speak English and understand some French – i.e. I don’t know that I’m even close to correct. But I would hit up vocab and basic grammar ASAP and you’ll be able to start jamming through stuff *really* quickly with regular use. You may also wish to email Koichi directly about this, he might have some insight. He’s usually pretty good about answering emails.

Best of luck! Maybe also share your conclusions when you get going?