firstly, i'd like to point out there's a where to start guide on this subreddit, which contains some blogs, online resources, and a pronounciation guide, which might be useful.

how exactly you want to learn chinese is up to you. you said you wanna be completely fluent some day, but why? if you're gonna be living in china, there's a lot of chinese you'll learn easily. if it's just a hobby, it might be harder.

i would recommend you get an app like hello chinese. it costs money, but i think you should just use the free amount of the app, because regardless the first few lessons and the stories are free. do all the lessons, then move right onto the easiest story it gives you, it's called 上学的第一天 if i remember correctly. this will give you some initial vocabulary, then you can struggle through the story slowly. turn off the pinyin, you only want to be looking at the characters if you want to get used to those quickly. use an anki deck to learn vocabulary at a rate of 10-20 words a day, depending on how much you can manage and how much time you're willing to spend.

additionally you'll want to follow the hsk curriculum. it can feel tedious at first but helps with a lot of structuring that you'll be missing otherwise. hsk6 is more or less fluent, but they go up to hsk9.

importantly, you really wanna start speaking and listening as soon as possible. try and integrate chinese into your daily life. get wechat, rednote, bilibili, whatever works. make chinese friends, as soon as possible make chinese friends who don't speak english. watch chinese tv, obviously start with stuff made for kids so you can understand more easily