For now, your job is to figure out how you want to study.
There are quite a few ressources for each skill that you’ll have to master.
You’ll want some kind of Grammar ressource, like TextFugu, Genki, Tae Kims Grammar Guide, Minna no Nihongo or A Dictionary of Basic Japanese Grammar. Some of those come with practice material and essential vocab, others dont. Using multiple ressources can give you another perspective on a certain topic, so its also worth considering.
I’d advice you to also take a look at Anki (Which is pretty much a flashcard software) and get an essential vocab deck for it. There are free Anki Decks on reddit, some of them complement certain textbooks like Genki. If you want to save time and actually remember your vocab, spaced repitition (Like WaniKani) is the way to go. Anki does that too.
Mentioning reddit, here’s a little starter guide from the Japenese Language Learning Reddit
Also, if you want to take Japenese Lessons (Probably best to wait until youre a few weeks/months in), you can check out italki. You can post questions over there and japenese people/teachers will answer them for you. (There’s some alternatives to italki, but I dont know why you’d need them )
Regarding your question when to start with grammar:
It really depends. When you’re deciding to use Genki, go ahead. It’s a good pacing and you dont need Kanji to get started. If you’re instead using Tae Kims Guide to Grammar (Which is free, so atleast take a look), I’d also advice waiting until youre a few levels in since knowing some of those pesky kanji will help
It’s really a tradeoff though. Knowing Kanji will help with your grammar studies, already knowing some grammar will help with your Kanji (Since you can use them and know some basic compound, verb and adjective guidelines)
There’s really no definitive answer to those choices, just what works best for you.
Turned out to be a lot more than I wanted to write, I hope some of it is helpfull
Good look with your studies