While I'm not very familiar with this proficiency scale, check out this site: https://learnjapanesedaily.com/how-long-does-it-take-you-to-reach-n1-n2-n3-n4-n5-level.html
According to that site, you can expect a minimum of 300 hours to reach N4; they regard these times as optimistic.
I found a plan here: https://www.quora.com/How-can-I-pass-the-JLPT-N4-in-3-months-What-apps-online-courses-and-textbooks-can-I-use
***I paraphrased the plan. Visit the site to see the full plan and to see other plans that others recommend.***
1. Start with Hiragana, and then Katakana.
2. Look for a standard N5 book. They recommend Genki (english-based) and Minna no Nihongo. With this you'll get a grasp of grammar and vocabulary.
3. You can now start with Shadowing. Search the internet for N5 level materials. It's likely to start with greetings. Do this 20 minutes a day.
4. Don't forget your Kanji! They recommend the Kanji Challenge book, with the pink cover. You'll learn the stroke order for the chinese symbols, and also vocabulary.
5. Once you've finished with the those, They recommend using the TRY N5 by ask books, so you can review and have a more comprehensive view of similar grammar points.
6. Try to do the sample tests for N5, particularly from the JLPT site.
7. Repeat the same process, for N4 materials.
8. Look for language exchanges in your country. There might just be a japanese person willing to teach you japanese, and that will be a huge advantage. Use sites like Hi Native, where you can ask about grammar points and words that seem like they mean the same.
Final note: You're set to go. For most people, this process takes about 6 months because it takes a lot of time to familiarize Hiragana, Katakana and Kanji. But you never know. Don't skimp on your shadowing practice, because although the JLPT has no speaking portion, you need to be able to speak the language in real life too.