If you’re looking for grammar, try Bunpro, everything is done in an SRS system, and the grammar is structured according to the JLPT.
For me, writing stuff out of useful. Textbooks can be a struggle to learn from, since once you’ve worked through them, you’ve forgotten a lot of points. That’s why I’m going through, writing out every example sentence. It’s probably a bit over the top, but it’s really helpful if you want to improve your handwriting/writing speed.
Writing out Kanji can be a huge help as well. A lot of the time, I won’t be able to remember the details of a Kanji unless I write it out. This isn’t so much of a problem for the first few levels where the Kanji is quite basic, but later on you will start getting similar Kanji mixed up if you don’t remember the radicals that differentiate them. The mnemonics WaniKani provides are usually pretty good at helping you remember, but I’d still recommend getting a Kanji writing notebook to practice them.
When it comes to self-studying, it can be hard at first to know whether you’re doing the right thing, and whether you’re doing enough of it. Ultimately, you should constantly be trying to read and listen to Japanese from various places. At first, this will be a struggle, since your comprehension is so low, but the more you do it, the better you’ll get. It will also give you a good idea of what you need to work on, and it can give you a boost of motivation when you suddenly understand something you had no hopes of understanding just a week ago.