I am also using Minna no Nihongo (I’m currently on lesson 6)! I would recommend potentially starting earlier than level 10, because I don’t think you really need to wait that long (I think I started at level 6, haha). If you have no knowledge of Japanese grammar at all, I would also recommend potentially watching some of Japanese Ammo with Misa’s grammar lessons for absolute beginners playlist on youtube, which made MNN much easier for me to understand. If you do insist on waiting to start the textbook, watching those videos could be a good use of your study time until then.
Regarding writing, yes it is possible to exclusively type the exercises and not write them by hand, but I would recommend learning at least a little bit about writing Japanese. I own the main MNN textbook and two of the workbooks, and what I do is type my answers into a word document for the main text, and handwrite my answers in just kana for the longer workbook (the text for that one is primarily in kana, so I think this is actually the intent with it), then try to write using the actual kanji for the shorter workbook, just so that I get a little practice with it. I’m hoping to eventually work up to writing my answers with kanji for both workbooks.
I know this reason sounds really silly, but it actually feels really good to be able to write in Japanese! And it uses different parts of your brain than typing on a computer, which can help your memory. As far as “efficiency” goes, yes learning how to write will be less efficient at first because you have to put time into developing a new skill, and it’s a skill that doesn’t immediately help you understand Japanese media, so you might feel like you’re wasting time, but it benefits you a lot more than you might think.
I have a few friends who are also learning Japanese, who are further along in their studies than I am, and I just found out that they all apparently have trouble getting the IME pad to work for them when they try to use their Japanese keyboard to locate an unknown kanji in order to look it up. I’ve had really great luck getting it to give me the kanji I’m looking for because I’ve been practicing writing kanji for months, and I understand stroke order and can guess the stroke order of unknown kanji and get it mostly right. Even though my friends know more vocabulary and grammar than I do, because they skipped the step of learning how to write, they never developed this skill.
The other thing that learning to write can help with is that it can help you interpret other people’s handwriting. If you’re only used to looking at typed kanji (especially typed kanji in primarily just one very clearly written font), handwritten kanji can look very different, which can throw you off. But if you have an idea of how stroke order works, that can help you interpret what is going on in the kanji, which can make it much easier to identify. I’ve heard people describe having trouble with 人 and 入 because they can look extremely similar when hand-written, but if you know stroke order, that can help you tell them apart.
And learning to write allows you to be able to take handwritten notes, which can also help you learn! Most of the research out there suggests that we retain more information from handwritten notes than typed notes. Personally, I take notes on the grammar that I’m learning, and I also write down the MNN vocab words with unknown kanji in them, because that process really helps me learn the words.
If you do wait another month before starting MNN, you could use the time that you aren’t using to work on the book to start to learn how to write in Japanese. Here are some PDFs organized by WK level that you can print off for learning to write kanji. I recommend at least trying it! The kana, too, take a bit of practice to learn (there are charts for those if you look them up), but once you learn them, it’s really not too hard to write full sentences in kana without having to reference any charts.
Starting to learn to write in Japanese is a slow and frustrating process because you feel like you’re back in elementary school again, learning extremely basic literacy, but it’s even more disheartening to be completely reliant on having a computer (and having a Japanese keyboard installed) in order to communicate in the language in writing. I think it’s very worthwhile to at least learn how to write hiragana and katakana and some kanji, even if you don’t practice all of them.
If I remember correctly, that Tofugu article says that it isn’t necessary to learn writing immediately, but it does think that it’s important to learn it eventually. I’ve seen a lot of people read this and interpret it as “never”! I think it’s fine for your writing skill to lag greatly behind your knowledge of vocab and grammar and kanji, but after you’ve gotten a couple hundred kanji under your belt and can easily read hiragana and katakana, I think that’s a good time to at least learn the basics of writing. You don’t have to learn every kanji, but the ones in the textbook are pretty common and probably worth learning.
From my own experience and from what I’ve heard from others, the Tofugu method is very good for getting a lot of knowledge in your brain very quickly, which can get you reading native materials faster, but the consequence of learning this way is that the knowledge you gain like this can also leave your brain very quickly if you don’t use it (just look at all of the people on this forum who come back to WK after taking a few months or years off and have terrible accuracy on their reviews). For this reason, I think there are some benefits to taking a little more time to be a little more thorough on some areas of study instead of trying to rush through as quickly as possible. You can still go moderately fast and see a lot of regular improvement without going at absolute maximum speed.
Sorry for writing such a long post! My personal speed is that it takes me about two weeks to get through a WK level, and about two weeks to get through a MNN lesson. Many people on this forum would consider that slow. But my comprehension of the MNN text so far is excellent, and the vocab and grammar are both sticking with me (I practice writing the kanji for several days while I’m working on memorizing the chapter vocab through Anki), and I’m able to keep this schedule without it interfering with the rest of my life. I also genuinely really enjoy studying this way, and I look forward to reading my textbook, and that’s important to me as well.
So, yes, it is possible to complete MNN while avoiding learning to write, but there are things you sacrifice in choosing to do so. In the short-term, sacrificing them can give you greater efficiency and get you to a point where you can read harder materials earlier, but if you want to truly learn the language and be able to use it outside of a few very specific settings, it’s important to learn writing at some point. So why not start learning the basics now?