If you really want to study japanese, learn hiragana and katakana first, it will make things a lot easier, trust me. Most of the content avaible out there have romaji (how to read with roman letters) these days, but as you progress, this can really hurt your reading with real japanese alphabet. It is good for the start, but not in the long run. For pronunciation, watch videos on YT to get it right, no mystery here. For kanji, it is good to learn a few from the start, like pronouns, some verbs and nouns. The basic. I learned the writing system first and I was already able to read examples in hiragana and some kanjis, so it was a big help. There is a lot of good content out there without romaji, so knowing the alphabet was good. But that just my opinion.

you do both at the same time, you learn how to write and pronounce the specific character you are doing. A combination of the two learning tools, sound and action, makes it easier to remember them.

learn both, practise oral language and study writing system too

I think that there are a lot of opinions about this. In my opinion, it depends on how you would like to get started with your Japanese. If you are currently in need of talking with native speakers, then practicing verbal Japanese would be more enjoyable and effective. If you are fond of Japanese books or relevant materials, you should follow your passion to read them, although this sounds very tough to many beginners, and so I recommend to read easy books written in Hiragana and easy and basic Kanjis. Reading and writing is likely to be a set. Learning Japanese writing system takes a long time, so you should take it easy. Many people I know start with basic Hiragana and Katakana. I have been learning English for many many years, and I now feel all the elements of language study such as Listening, Speaking, Writing, Vocabulary, Grammar study and etc, should go along as much as possible. Your choice can be made based what resources are most available around you. Please take it easy and enjoy the language by doing what you think you can be enjoying.