Not OP but here’s my personal opinion (and I’m sure many may disagree):

There’s a bunch of parts of learning a language (a few more for Chinese character languages like Japanese) and learning one often doesn’t help you that much with the others, which most people don’t realize:

- recognizing individual kanji characters

- recognizing words formed via combinations of kanji

- reading passages in context

- writing characters

- writing passages

- understanding grammar rules

- forming sounds naturally (people who can speak sound unintelligible because of bad accent, this is not the same skill as speaking - more muscle memory)

- speaking (does not actually require understanding grammar, nor sounding reasonable!)

- listening and understanding verbal language...

- without context

- in a casual context

- in a formal context

- with unspoken, understood context (this and above two require understanding culture)

- domain specific vocabulary (everyday speech is totally different than business, and different from speech with a lot of slang)

- knowing socially appropriate things to say or do based on unspoken context

- and more I probably missed

Learning all of the above is a project that people with decades of study can’t necessarily do all well [1] - so first pick what you want to be able to achieve and focus on that, and also acknowledge that learning a language is going to be a daily practice for the next several years of your life. If you don’t want that, then time spent learning a language will probably be a waste IMO (unless you’re just doing it for a general sense of Japanese language and culture - Duolingo is probably good for that), and I’d advise you to spend your time doing something else.

For me I wanted to be able to speak in casual conversations and everything else is secondary. That said reading passages is useful for understanding how specific grammar and vocabulary is used in context, so that was my second priority. Working in Japanese companies is legendarily terrible so I never had an interest in professional or very formal Japanese (just enough to understand formalities spoken to me when I go to stores or talk with reps at companies).

I’m currently at an intermediate level after ~1.5 years of regular study - good enough for most common social contexts, not good enough for business Japanese or niche topics. Someone deeper than me will certainly have different opinions as well.

- The first ~6 months, I liked the Pimsleur series but your mileage may vary. It’s old school mp3s (used to be cassettes) that teach you not by explaining rules but by giving you scenarios and having you use grammar rules and learn by inferring patterns, responding under time pressure (an mp3 can’t wait for you - this is important!). You will not have a formal understanding of the language but it can get you to saying things pretty quickly, and gets you over your fear of sounding dumb in a foreign language quickly since you’re speaking from the beginning. You learn some basic vocabulary and (sometimes overly formal) grammar, which will make more sense when you do formal study concurrently or afterward. It’s all audio so I just listened and spoke responses aloud to it during my commutes (by train, not caring that I look like a crazy person) and otherwise didn’t change my day to day life.

- WaniKani is great for learning to read individual Kanji and build vocabulary via spaced repetition (not the same as reading passages), worth the cost (every year they do a $100 off sale for lifetime fyi), though they play fast and loose with the meaning and composition of radicals so be aware of that - also its a fixed order, so if you take classes at the same time it will be out of sync with that. The open-source Tsurukame iOS app for it is phenomenal and I use it all the time on trains.

- Skritter is good for learning to write Kanji via spaced repetition (that’s a totally different skill than reading!), but to be honest you don’t need to really learn to write - predictive keyboards are enough for most people to survive, you rarely need to write anything down nowadays. I started using it more after enrolling in classes, since Kanji recognition was a core part of that. Their app is tolerable but not great - I bug them constantly to improve their iPad/Apple Pencil support, the closest digital thing to really writing on paper and pen.

- Bunpro teaches grammar points via spaced repetition, it’s pretty decent. The app is not very good.

- Learning from large group classes is good for some listening practice and learning grammar rules in general, but not that great for speaking practice because there’s usually too many other students to get that much opportunity to speak. You will learn what you’re doing wrong, but you’ll need to put concepts in practice much more outside of class.

- Learning by speaking to classmates in said classes... is not very optimal, since they don’t know what’s right or what sounds right either. Do it for your social curiosity or motivation, not for true language practice IMO.

- Learning from a small class or 1:1 will give you higher quality speaking practice - you can find pretty cheap teachers on services like iTalki. For getting grammar and usage right, I’d recommend real teachers vs random people on HelloTalk since the average person can’t explain grammar points well, but for getting to know someone on a non-professional basis/cultural learnings, the random person can be better (but if you have the option to esp once COVID blows over, IRL friends are the best).

- Getting a job in Japan can get you a decent amount of practice, though in a particular domain - probably formal, maybe repetitive

- Getting a significant other will give you a lot of practice in the specific domain of day to day conversation, but you run the risk of adopting the sound of the SO (guy sounding like a girl, in a very gender-segregated society like Japan, makes you sound funny lol)

- Immersion is not really useful until you can at least tread water so don’t think you need to move to Japan to learn - but like I said practice is important so maybe after 6-12 months of study it’s probably worth it if your life is flexible enough to make that happen.

- trying to understand movies/anime is hard to do until your listening skills are pretty decent, especially since they usually use a lot of niche vocabulary and grammar (talking like a samurai) not common in day to day life. You can try but I found that a steep learning curve for beginners. But you can find a bunch of well-transcribed stuff at FluentU and Animelon.

[1] A funny example: https://twitter.com/patio11/status/1247584725503332354