HTPC, NAS, whole house firewall...
Experience building. Take it apart, put it back together.
Now...take it apart again, put all the parts in a box. Leave it for 2-3 weeks.
Then put it back together.
Its easy if you take it apart, and have all the parts right there to reassemble.
If you leave it for a bit...then you get the moment of "Where did this go?"
A NAS, in this context, is simply a PC, attached to the network, with shared folder you can access form other systems. Doesn't have to be anything powerful, and storage size can be expanded as needed. Just add new drives.
My current house server runs on a Pentium G840, 4BG RAM, Win 10, and ~20TB in drive space.
And from your regular system, you can map drives with appropriate drive letters.
My "music folder" is the M drive. The movie/video folder is the V drive.
Stuff to be "shared" is the S drive. I can tell the wife..."Just copy that to your S drive." Poof..it saves to the house server, and I can see it in my "S drive" (mapped folder).