So as you may well know, i have recently started a course with BYU in which I can get a full high school credit for completing a "semester" of online Japanese. The best part is that I can finish the course as fast or slow as I want, which is sooo perfect because I already preferred to learn Japanese on my own time anyway. Here is what I've learned:
First off, if you already know at least Hiragana, GOOD, because it comes up fairly quickly and is tested in a way that would require someone who didn't know it to learn it/memorize it all. Therefore my knowing it made my fly through a section and feel like a BOSS. Once again, I highly recommend Let's Learn Hiragana by Yasuko Kosaka Mitamura.
Either way, don't worry too much because there are no deadlines (at least in my case) and as long as you have already completed some Japanese-oriented-self-nerding-out on the internets you should do quite well. I honestly think it'd be kinda rough if you had no experience/exposure to Japanese previously.
HOWEVER, that doesn't mean the course is bad if you don't know any Japanese, it just means I'm more comfortable with the sentence structure at first sight than you, not to mention a few particles and some vocabulary. SO, obviously the solution is quite simple: do some Japanese-oriented-self-nerding-out on the internets ^v^ Since you are most likely here because you're not entirely sure what you're doing, I've tried to compile all the sites I found useful in my fetus exploration of Japanese.