Yes, 2TB is plenty for someone starting out with digital music. Your understanding of the connection setup is correct. And you can indeed use a NAS for things other than music. My main computer is upstairs but I also like to work downstairs with a laptop. I originally got my NAS for music but ended up centralizing my data files on it – very convenient to work from whichever spot I want.
In the past, there has been confusion about what constitutes a NAS. WD and other companies make external hard drives and carry on about “personal cloud” and such, but these are not NAS units. The one you linked to may be a real NAS (I see it has an ethernet connection) but I cannot really be sure because the amazon site gives much hype and few technical details. I suspect, however, that it is not. They give no information about processor and memory, for instance.
A real NAS is independent of any other computer, unlike an external storage drive. That’s one of the things I like about it; in my setup there is no Win or Mac machine running. A NAS is actually a computer, albeit a low-powered, slow (by comparison with desktop or laptop units) one. Because it’s a computer, you install a server on the NAS. I like Synology units because they are reliable and their Disk Station Manager (the operating system) is both capable and easy to use. Synology also includes a server, called Audio Station. This is a decent program, but I prefer MinimServer because it is much more powerful in letting you display your tagging information the way you want. This is important for those of us who listen to classical music, but less so for other genres. You certainly could start out with Audio Station or the equivalent provided by other brands of NAS. QNAP is another brand that many people use, although I have no experience with it.
Among other things, a NAS is designed to run reliably 24/7, although you can set it to go to sleep after a certain period. The disk drive(s) that you install in the NAS should be designed for this kind of use; I have had good experiences with WD Red drives in my Synology. You can purchase a one-bay NAS, which is what I did when I started out. After I decided I really like streaming to the Bridge, I upgraded to a two-bay unit. In this setup the second drive is an automatic mirror of the first; if either drive fails, the other should still be OK. But in any such setup you need external backups too. Yes you do. Don’t neglect that if you value your music collection.
You cannot use foobar with a NAS, only if you are streaming from a Windows computer. If using a NAS, you install your server on the NAS and then install a control point on your tablet. The control point will locate the server and the Bridge automatically (you need wifi for this, of course). I recommend mconnect and BubbleUPnP control points; latter is android-only. There are others to try also.