You can build a HTPC a lot of different ways using a lot of different components. You seem to be talking about building a PC with its own internal storage. And that's fine, but here are the downsides to doing that:
Noise: The fans and the hard disk drives (HDDs) are the only moving components in PC. They make noise. For the fans you can pick and choose and get quieter ones. For the HDDs, not so much. The only way to reduce the HDD noise is by soundproofing the enclosure that holds them (often times, this is at odds with the cooling/fan issue) or by moving the drives away from the listening area. This is why you will see a lot of fanless designs used for HTPCs. Using a Network Attached Storage (NAS) component will allow you to move the HDDs away from the listening area as well, which is why many people use them. You will need a home network to use a NAS, preferably a wired network, but you can use a wireless network as well. Moving the HDDs out of the PC enclosure also means the overall size of the enclosure can be reduced, again, something many people desire.
Sharing: With a one piece HTPC set up in your listening location and no network connection, the only place you can access and control the stored music files is at that listening location. But if it were network connected, you could access music from any other point that is also network connected. For example, all my music files, both surround and the stereo formats, are on a single NAS box. Only my main listening room is capable of surround playback. But my wife and I also have several laptops and a few portable bluetooth speakers in the house. She may decide she wants to head out to the back patio and listen to some Zeppelin (which she often does). To do so she can take a laptop (which has a copy of KODI on it) and a portable Bluetooth speaker and access the NAS files. My son can use his phone to access the NAS and play music back through earbuds.
The network connection provides a lot of additional flexibility.
There are several threads in the tech sections at the lower end of the topic list that you can look at and read up on. Have a look.
Also, KODI has a great interface, so be sure to check it out as well. The thing that has prevented me from using Foobar on a regular basis, as well as JRiver for that matter, was the inability for either of them to provide on screen lyrics, which I really like. But now I see lyrics being shown on a few of the Foobar screen shots and I may have to look into it again. JRiver will not do that. The Foobar views can look great with a good skin, but the KODI screens are equally nice. The one I use (championed by Homer in the tech sections I spoke of) show an artist slideshow along with auto scroll on-screen lyrics while the music plays. The downside with KODI is no SACD ISO playback, but I convert that all to FLAC anyway.
- but I like the way JRiver just works well for video without a lot of screwing around, even at 4K with the latest version.
