If you want to try out different linux distros, I recommend using a VM and so you can get a feel for the experience and package systems. I personally use Linux Mint because it’s Ubuntu-based and I find the UI very intuitive coming from a Windows user.
For learning commands, there’s a ton of cheat sheets online and the basic commands are pretty simple. So like rm is remove, cp is copy, mv is move, ls to list files, pwd to see current directory, cd to change directory, etc.
If you’re going down the coding path then I definitely recommend learning git and vim as they’re really useful for source control and quick editing inside terminal regardless of if you want to use UNIX or Windows CMD/Powershell.
It's a max of 300 games that can be displayed on the home screen. You can install more but then you'd need to use FBI to see all the 3DS titles or twilight menu++ for DS/GBA titles.