These days I study by reading what I feel like reading, watching what I feel like watching, playing what games I feel like playing, and looking things up when I need to. Also I've been a bit obsessed with writing out 四字熟語 with a brush pen lately to practice kanji. In the past I used Anki, Remembering the Kanji, Tae Kim's Guide, and several textbooks.
There is probably not going to be any 'making a career' out of Japanese. It may supplement a career if that career involves business in Japan, but AI translation will take over the vast majority of translation work, or rather, already is doing so. If you want to be involved in what is left, you will need to be capable of very specific technical writing, e.g. patent law, medical research studies, etc., where the demand for accuracy prohibits trusting an algorithm anytime soon.
Some standard advice below.
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"What textbook should I use?"
"Genki" and "Minna no Nihongo" are the most popular book series because they are
pretty good. Because they are so popular, you can get the answer to just about
any line you have a question about by googling and it will already have been answered.
Genki is heavily preferred by native English speakers.
Minna no Nihongo has its "Translation and Grammatical Notes" volume translated
into a number of other languages, and is preferred by students who want
to learn in their native language or learn Japanese in Japanese as much as possible.
A Dictionary of Basic Japanese Grammar is a good companion to any textbook, or even the whole Basic/Intermediate/Advanced set.
"How can I learn Japanese for free?"
Tae Kim and Imabi are effectively textbook replacements, at least as far as providing grammar lessons. They lack the extent of dialogues and exercises in typical textbooks, so you will need to find additional practice elsewhere.
Erin's Challenge and NHK lessons teach lessons with audio. They are not IMO enough to learn from by themselves, but you should have some exposure to the spoken language.
Anki and Memrise both replace flashcards, and are general purpose. Koohii is a special-purpose flashcard site learning Kanji the RTK way.
Dictionaries
"What can I use for reading practice?"
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WEB版「エリンが挑戦!にほんごできます。」サイト閉鎖と新サイトのご案内 | WEB版 エリンが挑戦!にほんごできます。 (online audio-visual course, but has 'manga' version)
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https://tadoku.org/japanese/en/free-books-en/ (Graded Readers)
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https://www.japonin.com/free-learning-tools/teachers-blog.html (Essay style blogs from Japanese teachers)
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https://www.pixiv.net/en/artworks/80636366 (Crystal Hunters Manga "自然な日本語版")
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https://www3.nhk.or.jp/news/easy/ (Easier versions of the news, with links to the full version if you are up to the challenge)
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http://hukumusume.com/douwa/ (福娘童話集 - collected folk & fairy tales)
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https://www.aozora.gr.jp/ (青空文庫 - public domain works)
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https://syosetu.com/ (小説家になろう! - Web Novel site for aspiring authors)
"What can I use for listening practice?"
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Easy Japanese 2015 - free lessons with audio drama | NHK WORLD RADIO JAPAN (NHK lessons - online audio-visual course)
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WEB版「エリンが挑戦!にほんごできます。」サイト閉鎖と新サイトのご案内 | WEB版 エリンが挑戦!にほんごできます。 (online audio-visual course, many skits)
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https://www.japonin.com/free-learning-tools/teachers-blog.html (Essay style blogs from Japanese teachers)
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https://jlptstories.com/ (JLPT Stories podcast)
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https://www.youtube.com/channel/UC0ujXryUUwILURRKt9Eh7Nw (三本塾 : Lessons and conversations about Japanese, in Japanese)
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https://www.youtube.com/@nihongonomori2013 (日本語の森 : Japanese lessons in Japanese JLPT focused)
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http://nihongoconteppei.com/ (Easier Podcast from a Japanese teacher)
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http://teppeisensei.com/ (Harder Podcast from a Japanse teacher)
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http://hukumusume.com/douwa/ (福娘童話集 - collected folk & fairy tales, many have audio)