I imagine interstellar coalition governments probably function a lot more like the EU than a single country. Individual planets/solar systems would probably function under a somewhat independent governorship that is still subject to the overall laws of the federation/republic.
It's sort of like asking "how big can a city get?" before states and nation-states existed, when in reality at some point a higher tier governance inevitably takes over. An interstellar or galactic scale government is necessarily going to be massively stratified with many levels of hierarchy in between. I think this is why many sci-fi governments at this scale are also described as bloated, unintelligible bureaucracies.
I don't have any revolutionary advice to give to you my friend. I'm quite a bit younger than you and I already am feeling the creep of losing touch with the speed of new technology. I think to a certain extent that is inevitable. I will say that there is a tremendous amount of survivorship bias in the videos of young people making racks off of day trading. These videos are designed to get people hooked on what is functionally gambling. No offense meant whatsoever, but if you're living paycheck to paycheck it's the exact type of slippery slope that can turn a bad financial situation into a ruinous one. I hope you find something that you like though and wish you the best of luck in whatever you do!