It's good that you've got some enthusiasm for learning Japanese! Let me tell you, one of the most important things you could possibly do for yourself is to try and maintain that enthusiasm no matter what. You need to really ask yourself if you're patient and willing enough for as huge an undertaking as learning a new language, because it's going to be incredibly lengthy and frustrating, no matter how good of an attitude you have.
As nekojita said, learning a new language isn't something you can ever really be "done" with. After all, even your vocabulary and understanding of grammar rules in English can be expanded upon at this stage, even though (I assume) it's your native language.
It's definitely not linear, and there isn't really any "correct" way to go about picking up a language, so just about any place you go to find some sort of guidance is going to be a help. For that reason, I encourage you to look around, and never stick to just any one method or system of learning. There are many different language-learning resources out there, but most of them will focus on different aspects of the language. Some might focus on grammar while others might focus on teaching you open-ended words which will be easy to use in a lot of situations.
Personally, what I did (and strongly recommend you try) is getting the iStart Japanese (Might just be called Japanese now) app from Mirai Languages on the iOS, if you have any iOS devices. It isn't super useful for gaining a big vocabulary or learning about grammar rules in-depth, but it teaches you a tiny bit about a lot of different aspects of the language, so I think that it'll give you a general idea about what Japanese is like and how it works. I never got past lesson 25 (out of 50 for the paid version of the app), but just the first few lessons really helped to kickstart my learning.
The next thing I'd REALLY recommend is Pimsleur's Japanese lessons. Basically, it's just a bunch of audio recordings you listen to, and they'll teach you Japanese. I've never tried any audio system other than Pimsleur (unless you count iStart Japanese), but I feel like it's a very detailed and nuanced system. My Japanese vocabulary is over 500 words, mostly because of Pimsleur. It helps you to understand the grammar and language as a whole by teaching you a small handful of words, how to string them together in a sentence, and then teaches you MANY grammar rules by building on what you've already learned. All in all, it's a pretty painless experience, considering how much you're getting out of it.
I hope this helps! My Japanese isn't very good at all (I wouldn't call myself more than just a beginner) and I don't know about all of the best resources out there, but feel free to message me if you ever want any personal help. At the very least, I can tell you how I've gone about learning what I've learned since it's still very fresh and new in my mind.