Me and my GF are currently doing this. Some recommendations from personal experience:

• Pimsleur is really nice for getting from 0 to being able to speak and understand some amount. It’s very much less overwhelming than jumping head-first into grammar. You can find torrents for it. It’s also a really good way to learn to listen to and speak Japanese out loud, something most other resources lack.
• everyone recommends Genki, and I concurr; it’s a good book series on grammar, with plenty exercises. Will really help filling in the gaps where you have gotten a feeling for things with Pimsleur, but are not able to grasp the underlying concepts intuitively.
• don’t shy away from Hiragana and Katakana. They are easy to learn (seriously, spend an afternoon on each and then do kana.pro for a week and never look back). Ignoring this will prevent you from using most learning resources.
• use Anki; again, everyone says this, because it’s true. You can download a pre-made pack for Genki. 10-15 cards a day are a good leisurely pace, allowing you to tackle a new chapter in Genki approximately every 7-10 days.
• don’t fall in the rabbithole of watching YouTube videos on learning Japanese. Just study instead. If there’s a concrete thing you struggle with, look for a Video on that topic. Most of the geberal advice videos seem to come from English-speaking folks for whom Japanese is their first foreign language (which is great! Don’t get me wrong!), and the resulting information ranges from obvious to questionable.
• decide if you want to learn Kanji (if you don’t know them anyways, given your stated experience). I’d recommend it. It’s actually quite fun, and if you want to watch Anime in Japanese, there’s a good chance you’ll have to use Japanese subs for a while to help along anyways…
• most people online seem to suggest only learning to read Kanji, because “you never need to handwrite things today anyways”. I call bullshit. It’s marginal additional effort, can actually help you with recognition, and if you ever end up needing / wanting to write by hand, you’d have to start all over otherwise.

Lastly, no, it is not a waste of time. Apart from anime, a new language means new ways of thinking, of challenging yourself, of being able to experience people and culture through a new lense, and potentially increasing job opportunities.

Plus if you ever end up visiting Japan, it really comes in handy.

Feel free to ask any followup things that I’ve forgotten about…

Edit: I forgot to mention: I am nowhere near fluent yet, and do not claim the suggestions above as “ultimate Japanese learner advice” or anything like that.

Also, very quickly you’ll start noticing phrases, words, topics when watching anime or japanese videos or music, even if you can’t follow the full conversation. That’s what really motivated and kept me going early on.