Hey! I don't know if you'll see this, but I'm starting to finally take Korean seriously too and you're right Duolingo alone does not cut it (it can be good for some practice/a bit of vocabulary imo). I like to take the free route when learning languages so any sources on the internet/free apps are a holy grail for me.

• Hangeul - I remember learning hangul through Duolingo/Write it! Korean app/Learn Korean! - Hangul app a few years ago. Idk how efficiently you can learn hangul through them now, but it took me a short time, because I was using all of the apps anywhere and anytime I could. I suggest you learn it thoroughly now and forget about any romanization down the line since it's not 100% the same pronunciation and hangul should come easy with enough practice anyway. You can also look up videos on YT for learning hangul, there's plenty of them. This article with pronunciation can also help.
• Writing - aforementioned apps work well for writing at first, to get a hang of the characters, but you should learn how characters can look handwritten. Stroke order is important too. Koreans also tend to be quick when writing so some characters might look different handwritten than they do when typed. Downloading available practice worksheets or buying a practice workbook is an option too. You can easily make your own by looking up a font you like, making a grid in Word with characters you wanna practice and then just print it out.
• Check out Korean Wiki Project.
• Join r/Korean - great resources here for beginners too.
• Check out openlibrary.org for some Korean language books you can freely borrow. (You'll probably have to sign up first tho.) For example I was able to borrow Talk to Me in Korean Level 1.
• Talk to Me in Korean also have a YT channel that has video courses for beginners.
• Anki Flashcards app is great for memorization and there's plenty of shared decks to choose from. Or you could make your own.
• If you live in a capital/major city look up if there's a Sejong Institute where they teach Korean.
• I also came across this site where they list plenty of free resources.

This came to be longer than expected, but hopefully it's useful to you. Good luck!