All the NAS boxes I've seen are wired. This means that you have to connect it to your Mac via an ethernet cable. The upside is that the NAS can be very far away, if it's possible to run a cable there. For example, mine is two rooms away.
There are variations, but here's how mine works. It's old (D-Link DNS323), but I don't think there are fundamental differences between it and newer ones. (That's not to say that newer ones aren't better -- surely they are.)
It's a 2-drive box, but can work with only one. When I set it up, I gave it a name and a fixed IP address. It's called "colden-nas," a remarkably unoriginal name, and has an IP of 192.168.0.41.
I set it up and occasionally maintain it through a browser. But that's the only time a browser is needed.
It appears in Finder exactly as named, under "Shared Devices." If I click to open it, I see "Volume_1," which is the disk itself, and "web_page," which is if I need to maintain it. Click on "Volume_1" and there are my folders and files.
I copy back and forth exactly as I would for any device. It's all gigabit, so it's acceptably fast.
I'm running Mountain Lion. ML rarely drops the NAS from my finder list, but sometimes it does (Lion did it all the time, as did Snow Leopard). When that happens -- when I see it's no longer there -- I just give command-K at the keyboard, and choose whether to mount either 192.168.0.41 or colden-nas. In a moment it comes up and I'm good.
It's very convenient, but I don't know that it would be that great as a desktop housing for that spare drive of yours. It doesn't sound to me as though you need it to do what it does best -- operate remotely.
No wireless connection available now is going to match gigabit ethernet, so I wouldn't bother trying to go wireless for this.
Several weeks ago I picked up one of these:
http://eshop.macsales.com/item/Newer Technology/MSQKIT0GB/
and I've been very pleased with it. It has FW800 and USB3 and eSATA as well. And the price isn't bad at all.
That's what I'd recommend. You can use FW800 now, and if you get something with USB3, you'll be good there also.
Oh, and the answer to the dual FW ports is that you can daisy-chain FW devices. So for example, you can go Mac-->FW device 1--> FW device 2. Both FW devices will be available from the Mac.