I would say go away from reliance on romaji, japanese written with roman letters, as fast as possible and dive into kana, the syllabic/abugida alphabets, with more emphasis on hiragana because it's more practical. Start learning grammar structure and get familiar with the patterns while you learn more words. Some people take the most used words from frequency lists http://en.wiktionary.org/wiki/Wiktionary:Frequency_lists/Japanese though learning from what you're interested in and find through flipping a dictionary might lead to more retention, because memory is related to one's excitement on what they're learning. If you get excited about shoving your nose in a text book (I certainly do), the series I have experience with that also work well are the Genki books. Sometimes people learn the best through only immersion in media and things that are exciting and relevant, which would be an accelerated path but probably best supplemented with a structural method, or at least something solid to bounce back to. What are you in to? If there's a particular passion you have, maybe you can find japanese texts/video/etc related to it and translate bits at a time after getting some grammar and the kana down and picking up kanji (should be a constant). Although it can be a bit intimidating and time consuming to go full in, especially with a language that has 2,000+ common characters and a very fast spoken style. I have a phone app that recognizes kanji, but the stroke order is imperative for it to work. Learning proper stroke order is important, and how kanji are structured by their pieces, their radicals. Complex kanji are basically made out of more simple kanji; just like how english words are made up of usually simpler root words in a line, kanji is the square version. Some grammar stuff: Japanese is a Subject-Object-Verb language. Hope this was helpful and not too rambley. Definitely follow what you get excited about.

In my opinion, 4 hours is a long time to study for a beginner. Studying many times per day for a short periods is more effective (at least for me). For example, half an hour in the morning, half an hour in the night and so on. Also, study according to a specific book or a website, don't just study what you want because that wastes your time. Since you can understand Arabic, I would recommend this forum where you can find too many resources for learning Japanese. http://www.ogurano.net/JpAr/ Hope this helps.

To learn hiragana, I used a chart, whited out the symbols but kept the English sounds. I then photo copied a bunch of these, filling out as much as I could remember, than filling out the rest. I did this for one weekend and nailed hiragana.