That can change depending on the type of projects you’re working on,
To be really effective, you need at least 2 different copy, so if ones broke you don’t loose your data.
You can also store you backups on a cloud.
How files are organized ?
That should reflect how your projects are organised, I’ve got a folder for each client I’m working for and a folder for each projects . Once a project is done I get rid of all unnecessary files and I archive the project folder. In my archive drive it’s the same organization , One folder per client that contains one folder per projects.
I use an external disk drive to store data at home, and at work we have a more complicated setup to be able to store more than one copy of the archives.
The good practice in your projects is to separate the data from start so you can easily get rid of temporary files. I work in animation so we only keep the .blends, textures, and final output. So instead of keeping 1To of data, we can strip it down to ~100/200Go .