What is your end goal with this? Going for BSc in Computer Science / Engineering would enable you to become a developer / computer scientist.

Photo/video/vector editing seems very out of place in your plan. That's just another domain. If you're passionate about those visual arts, that's great and more power to you, but know they're not relevant for a computer scientist. Src: I've been there.

Regarding everything else you've said, it seems to me that you're learning stuff without a direction and just because you've heard those things (cs50 / linux), are important. I suggest you choose a moderately difficult task (game, app, tool, website, ehatever) that seems interesting for you to create, (install linux) and start working on it, and focus on finishing it. You'll learn a lot on the way and gain a broader understanding of how a project is pieced together. Most importantly, you'll figure out what you don't know, and thus eill have a direction going forward.

And don't get me wrong, you're right, you can gain a lot of valuable knowledge by going through cs50 or learning to use the linux terminal, but it's not really useful unless information, unless you apply it to a project.

There seems to be a general consesnus that feddiverse users don't want anything to do with meta and that instances will defederate with threads. I'm curious if the majority will follow this trend to avoid yet another EEE, or if there will be some exceptions. I bet meta will be open to pay good money to instance admins for "colaboration" if the instance is big enough.

As other poster recommended, you should by all means install Linux and learn by using it as a daily driver.

With that budget you should be able to get your hands on a machine with plenty of power. My recomendation would go to a lenovo t480/t480s. I was planning to buy one of those for myself but my current laptop is still good enough. Regardless of the device you choose, I would recomend portability over power: power efficient i5 4 cores, 8gb (idealy 16gb) ram, ssd storage, lightweight and good battery.

To answer your last question, you shouldn't be concerned about performance. Linux can give life to old hardware, but you're not really looking at old hardware.

As a cybersec student myself, I would suggest starting out with a generic linux distro and just install the tools you need as you go. If you really need kali, install it in a vm. I say this because I expect you'll use Linux as your daily driver, and Kali is NOT mean to be a daily driver, but a tool for when you need it. And "when you need it" will come with experience I guess.

Mint is a very good start! If you don't like it you can always switch later

I mostly use a gui file manager, but when I do use a terminal based one I use ranger. Haven't tried others, I just like this one.