Are there any good online courses or tutorials out there that can teach me MQL4 programming for creating my own custom indicators or expert advisors in MT4?
There's no course that'll come anywhere near you plus a few hours of GPT 4 developing things that you need. Start really simple and you'll pick up 95% of it as you go, the rest you'll have to look up. It starts really slow, but I'm a month in, and can now do stuff I thought way too complex to even brief devs on. It's tremendous.
If you are going to start learning that language try the latest version. https://docs.mql4.com/mql5_language