There are hard drives specifically made for video, but they are talking about recording a video, think security camera feeds, etc... Rendering is a very different animal. Having said that though, today's faster hard drives should be able to keep up with a typical rendering system. So I would store the video (all data actually) on the hard drive. What you do not want to do is to fill up your SSD to its limits. They need free space to function properly. Basically, a full SSD is an unhappy SSD, which will then lead to an unhappy you.
As far as what to buy, I prefer HGST, Toshiba and WD, and in that order. The seem to have the lowest failure rates for hard drives. You will know better than I will about how much capacity you are going to need. Just available hard drive that has 3GB. For some reason 3GB hard drives seem to fail at far higher rates than 2GB or 4GB drives overall. I would also try to get at least a 64MB memory cache, and 7200 RPM drives for this.
As far as rendering to the SSD and then copying, I do not think you will see much, if any, benefit from doing that. But that does depend on how fast your rendering program can produce its output. But my understanding is that rendering is slower than just plain capturing a security camera feed. And a hard drive can do that easily. So I would put all of my video on a hard drive or two. Maybe you could put raw video on one hard drive and write the finished output to a second hard drive.