I recommend you start with some basic linux education, there are tutorials on line, and there are books available for reading. Arch Linux targets and accommodates competent GNU/Linux users by giving them complete control and responsibility over the system.
https://wiki.archlinux.org/index.php/The_Arch_Way The questions you are asking make it clear you don't have the background knowledge to do what you are asking. If you want to realize the vision you posted above, it will require you do a bit more education so you have the basic understanding to do what you want. What you want to do will require a better understanding of the linux workings. I started from about the same place as you a couple of years ago. I bought a couple of books, and read a lot of posts, and did a lot of google searches before I was ready to put all my data on a linux shared drive.
( once nice thing about the Archarm, is that as long as you don't mess with the uboot, you can set it up and experiment until you figure it out.) ( just make a backup USB stick)
Tom