I personally do Judo, so I would say martial arts can help, especially because you constantly hear the words repeated. There are lots of judo instructionals online for free, some with subtitles. If you can translate this to English that would be great ;).
Katsuhiko Kashiwazaki - Newaza of Kashiwazaki - YouTube
For hobbies I generally use wikipedia to pursue knowledge about subjects (Japanese wikipedia is huge).
I take lessons of Japanese in Slovak and it made me appreciate I do have some functioning Slovak. I would say after a while try and get language instructionals in Japanese if you want to learn another language.
You can use Improve your Japanese pronunciation using YouTube (youglish.com) to search for any hobbies, like how to put up a shelf or origami.
I personally use core texts for any language, the famed polyglot Emil Krebs did this with the bible (probably other stuff too). I personally use Bill Bryson´s A Brief History of Nearly Everything as it has the fundamental sciences we all know. Then I am starting to look at diary books like Diary of a Wimpy Kid, will hunt for something like Adrian Mole later. Kid´s encyclopedias are really good as well as they are written in such a way pretty much all people in that language have learned.
I would then personally look at Japanese literature and try to find a famous Japanese book from the past 20, 40, 60 and 100 years as quite likely these have had an impact on the Japanese language. I am now reading The Red Room in Swedish, but I will get an English translation to make sure I see how it gets translated into English because understanding what is said in a language often doesn´t quite get across the “social” context. For example most English speakers know what a black tie dress code is, but perhaps don´t realise what they´re reading in Swedish is the translation of this and think both things are seperate terms for different types of formal wear. They in fact say “smoking” which comes from English “smoking jacket” where people used to wear a special jacket to smoke in because they only washed once a week or so. Smoking – Wikipedia The first time I read “smoking” I thought “ok, it is to do with smoking jacket” but I didn´t think it meant black tie. This comes from a period where the upper class was generally very internationalised and conventions were put into ettiquette guides. I am quite certain (as Victorian culture was popular in Japan) a similar set of ettiquette guides exist in Japanese, using English/European loan words.
If you are pursuing a hobby and ARE ALREADY good at it in your own language, make sure you use things like Wikipedia to hunt for it in your language, then click to the Japanese. Other than that you need a native speaker who is wise to ask questions to. A core problem you have is believing every native is an expert in their language, and they´re not. So whilst you can learn with natives, you can´t often ask them a question which makes sense. My grandfather was good at Italian, he knew an Italian guy at a restaurant and would come in and talk to him with his 18th Century Italian classics vocab, and the chef would always laugh and say “Where did you hear this word? I don´t even know it…” he got valuable feedback (not every Italian knows those words) but he couldn´t ask him for Italian language tips as the guy was a “black box” operator.
If you´re learning a hobby you´re not good at in your own language, you will have to accept the fact you will probably need to learn about it in your own language too. Otherwise you´ll come across a lot of misconceptions about what words mean or how they can be used in different contexts.