I think the biggest part of learning Linux is learning where to get help. Most programs have a help dialog with --help or -h, or man pages you can find somewhere. Even the terminal has a help dialog if you just type "help", most things are more user friendly than they seem!
If man pages are difficult to read, I recommend installing tealdeer (tldr). it shows a short summary of example command usages and it's great (e.g. tldr ls shows the different ways you can use ls)
depends a lot on your actual hardware. some 2014 computers can run kde just fine, some will struggle with it. what actual components do you have?
I have arch + kde plasma running on a i5 3320m among other things and it's completely fine. Your 4gb ram is not an issue.
The biggest issue around this generation would be if you have a spinning hard drive, you'd want to replace that even with the cheapest used ssd you can find anywhere asap.
Arch is fun and you should try it at some point but it's not "faster" than Debian or mint or whatever, it mostly just comes down to your desktop environment and web browser.
if you want to customise everything you can do that with .inputrc configuration in bash