Brand New, Need some guidance

Hey, I'll keep things short and go straight to the point, if you want to skip to the questions, they're at the bottom. I'm not interested in making money, I just want to make a genuinely good piece of software many can use.

I'm brand new, have never touched coding except for a week watching HTML and CSS tutorials for Web Dev. I'm ready for the torture that will ensue, it's just a fun project to make during the summer.

I want to make a software, full-stack, Similar to Discord or TeamSpeak (not a discord clone, just better) reason being I'm sick and tired of seeing cool features being locked behind a subscription fee, so I said "fine, I'll do it myself". I'm well aware that I'd never be able to beat an entire company filled with hundreds of programmers that have done this since 5 years old and have made their own programming languages at 7, but I digress, might as well try and it'd be a cool project to add to a random resume (although I plan on becoming a 3D artist)

Wanna make it open-source so anyone can help or make any additional mods to it. I want it to be an app you can download onto your computer and use it like any other app like Steam or anything Adobe ect. Not strictly on a browser.

Questions: -What should I know before committing to this project? Things like cybersecurity, keeping the users data secure, how to make voice calls work ect. -What languages should I use for the front-end and what languages should I use for the back-end? -Should I watch those hour long tutorials or read things off of the documentations and jump head first into this pit of chaos? -If I end up actually committing to this project and releasing it and starting a Start-up or a "go fund me", what are the headaches of making such an app international? The headaches of marketing?