I've used both Xubuntu and Lubuntu, and both are awesome for old machines. Good luck! :)

The question is: What are you building? Do you want it to be a SPA(Single Page Application)? If answer is yes, you can go with any popular JS framework. Three most popular these days are: React, Angular and Vue. All three are great, so it's only about personal preference. This way, you'd be building an API with Rails and later accessing it in your SPA. If answer is no you can render your app on server using some templating engine which is compatible with Rails environment. My advice to you is to google those and see what you like the most.

I guess I always forget what it's for, and when I realize what it does it's easy to use so I end up checking them every time :D

I'm googling over and over again for substring(), split(), slice(), splice() and similar, every single time I need them :D

If you want to have some kind of structure for your css you should check SMACSS, OOCSS and BEM paradigms. These are cool, and will give you proper direction if you want to write better CSS. I'm not using SMACSS and BEM all the time because it's not always necessary but I like idea of OOCSS very much, so I feel like I always write modular CSS. Commenting might help too. There is no answer for how to write it correctly, it's up to you to discover how you like to organize code :-)

Well, I can give you insight how I tend to learn and what works for me. Whether it's video tutorial or not, I look at it few times in a row to get bigger picture of how is something supposed to work. I don't dive into details immediately. I simply want to understand. To google is perfectly okay , remember this! You can't memorize everything, and you should not. If you start preferring one framework over another you will get used to it, and you will code some parts without googling it, but you should never force yourself to remember things. It will come naturally if you are persistent with your technology stack. BUT, I think you should always seek to understand, that's quite another . The more you use technology the better understanding you will have. You can't really understand it unless you use it. Just be playful, that's it. Kids are very good at learning, you know that. They learn language very fast, they grow in every single way, because they are not afraid to explore. They take it as a joy, and so should you :-)

So, with that in mind, I assume you are going to have 2 separate servers. One for serving Angular, and one for Koa and database. Am I right?

Thank you Sir! I have to say, this is one of the best looking apps I've ever seen, and it's very fluid and interactive at the same time.