How should i build or buy a NAS?

So I'm a data science major and love to do my own hosting for obsidian for note taking. I want to be able to upload thorugh my phone when i'm at school or at work. I want to also build it and understand how it all works because it would be a great skill. What do you guys think? I have a lot of files of personal informaion and all sorts of things and books and lectures that i just don't want to lose. I want to also do some AI on it and run a media and also have family members use it as well like their own google photos into it. The only issues i see with this is electric bill maybe and also will it break and i lose everything.