Hi, so I was talking with @chevalierlorraine about excellent resources for learning Japanese so I thought I'd share what I use/used here!
The #1 textbook for learning Japanese is the Genki series. No contest. I would slam-dunk every other textbook directly into the trash if I could. And then fire that trashcan straight into the sun.
This is a COMPREHENSIVE lesson format, where you will 1. Read dialogue, 2. listen to dialogue, 3. Learn the grammar and vocab from the dialogue, 4. Do exercizes to better ingrain the grammar, vocab, and spelling from the dialogue, 5. In a classroom setting write your own creative dialogue using the grammar and vocab and then memorize and present it aloud (tbh do this anyway even if you're solo!), 6. Be tested on the grammar, vocab, and spelling. Rinse and repeat each chapter. Each textbook is one year of Japanese study, so Genki I and II will take you through two years of study.
Comprehensive lesson formats are THE best way to learn things in language arts. Japan traditionally breaks things up where a year will be nothing but vocab, the next year only grammar, the next year only speaking, etc., and this is why no one fucking learns English there because they are never synthesizing information nor given the opportunity to put the language to use for *themselves* to give it value. This janky, broken-up format, however, is what you tend to find most when looking at Japanese textbooks because it's all the professors know. It is bad. Genki breaks this mold by teaching every skill together in a comprehensive format and is extremely effective at making things stick- especially if you make sure to do the creative writing portion, even if you are studying on your own. I can't emphasize enough the importance of creative writing exercises.
Genki comes with a companion workbook as well. When you begin Genki II, you can also begin the classic 1,000 Kanji workbook:
There is also a "Basic Kanji Workbook" divided into two volumes with 500 kanji each, but most of those you will have already picked up in Genki I. It can be a good refresher, though.
If you can master both volumes of Genki and this kanji workbook, you will have a solid foundation for basic Japanese and will be ready to work on your year 3 textbook:
These photos are terrible quality but they are published by The Japan Times and run in a format very similar to Genki and also comes with a companion workbook. You can also begin the next Kanji workbook for advanced kanji:
For dictionaries, Kodansha's Kanji dictionary is the gold standard, although I also really like Tuttle's as well and recommend getting it (you can never have too many dictionaries tbh). I will also include the general dictionary I used for years, published by Random House.
Again, you can never have too many dictionaries, because some dictionary will always have words in it that another doesn't, or may explain things in a specific way or have some feature that another doesn't, and the more information you have to synthesize in your brain the better.
I also studied Bungo/Classical Japanese (think "tale of genji" in the original text), but that is a different can of worms and a harder to get set of study books with no space to talk about here. However if you find yourself interested, I recommend getting into Bungo at least a little bit because it can also help you with some Japanese dialects. I met an old man at the base of a huge mountain in Hokkaido who spoke using Bungo grammar who I would have never been able to understand if I hadn't taken that class. After a talk with my supervisor I later found out that was NOT a normal old people encounter and I am now fairly convinced I encountered the mountain kami and was nearly kamikakushi'd if it hadn't been for my Irish ancestors screaming in my ear in that moment to not accept his fey invitation to go up the mountain with him. xD
If you can master all of the above (minus the Bungo), it is quite literally all you need to plop yourself down in the middle of Tokyo and start applying what you've learned in a real life setting. If you can afford to spend some prolonged time in Japan (say, a month- air bnb is shockingly cheaper in japan if you book a month at a time than just two weeks), you can start adjusting the "textbook Japanese" you learned to make it more "real world japanese" if you're willing to put yourself out there and participate in social activities like going to lives, hanging out at hole in the wall bars, loitering on the street sharing cigarettes or lighters with people (even if you don't smoke, always carry a lighter in Japan!), etc. If you can make friends this way, those new friends will end up taking you all over the place while you're there, so don't be afraid to get out there. I would just personally say to avoid Roppongi, and if you see any Big Out-Of-Place Dudes "guarding" the outside of any shop (you will know what I mean when you see it), hey don't go in there! you are going to have a Bad Time and end up as a news bulletin on what not to do from your country's local consulate lol. Also do not let strangers drag you into any establishment because you will also end up a consular news bulletin. Ok that's it for my safety tips.
If you want to venture outside of Tokyo, no textbook can prepare you for that and you will need to prepare to stay in your chosen town or city longer in order to learn the dialect spoken there. It took me 6 months in the Kansai countryside before my brain rewired itself to understand and start using Kansai-ben for example, and I had 4 years of formal Japanese education, including a year in Tokyo, under my belt.
If you can't go to Japan yet and would still like some good, real world listening practice, I recommend tuning in to NHK's free snippets of daily broadcasts- 6am-8am and 5:30pm-8pm are prime time in Japan, but morning often has the most importance placed on it. Watching clips from Ohayou Nippon used to be openly available but it looks like NHK has decided to gatekeep it these days (jerks). However, regional news clips are still free to watch. Check out https://nhk.or.jp/nagoya/ to get started with watching news from Nagoya.
In Japan the general goal is to keep the complexity of news stories at about a 6th grade level but they do use a lot of compound kanji phrases. News stories are often about simple things like water mains breaking, community activities, one day I remember the top story was some kid was going around smashing mailboxes one week lol. Occasionally it will be something serious like someone getting hit by a car, or the yearly family homicide. Japan is an extremely tame place and it's only a couple times a year something truly spicy happens there, but under Takaichi Sanae a lot of anti-foreigner rhetoric has been stepped up in the news lately when previously "petty crime"-level stuff, no matter who perpetrated it, would have been ignored by the press as not being newsworthy, but thanks to the Japanese government having, literally, a 1% stake in NHK, we occasionally have to put up with short bouts of "bad foreigners"-focused stories, the perennially occurring stupidity that is the Dokdo/Takeshima island dispute (extremely, extremely stupid), and pretending that absolutely nothing is going on at the Fukushima Daiichi reactor since Abe's government made it illegal to report that it has been dumping gallons of radioactive waste into the ocean for over a decade now. Well, it could be worse lol.
Anyway, because of its simplicity and usually tame topics, watching daily NHK news clips can help with listening comprehension, especially if you can get good at taking notes about the words you catch that you don't know and can look them up after. If NHK feels too hardline, you can also check out Fuji TV/Fujisankei which has a bit more freedom in their reporting.
And that's it! There aren't really any "online resources" I can recommend. I think if you find yourself not fully understanding a grammar point that sometimes sites like Tofugu and Maggie-sensei can offer alternative explanations and examples that can sometimes be helpful, and if you're in a pinch Jisho.org is a solid online dictionary, but Genki is pretty great at explaining things in an easy to understand way and should be all you need. Remember to keep it simple! 80% of the battle of Japanese is sussing out the logic of what you're looking at as literally as possible and then rewiring your brain to accommodate and learning to 'live' with that new logic, so sticking with the same system starting out so you don't get too overwhelmed or confused by too many voices will help you a lot.
I hope this has been helpful!! Happy Learning!!