Yes, this too. Only reason you'd ever use 5,200 rpm hard drive is for big storage of something you don't use often, like media files on a home network or messes of documents for a business.
A good comparison video of 5200 rpm speeds vs 7600 rpm speeds:
LINK.
MoLoToV : ever tried one of the 10,000 rpm drives, the WD Raptors? Those things were pricey, but blazing fast. They were SSD's before SSD's; too bad they're now basically obsolete due to the improvements and prevalence of SSD's, but they're still cool.
That really depends on what you want to do with your hard drive, and how you want to configure it.
The way you described the set-up in your original post, you planned on keeping your old hard drive that already has Windows on it and simply add this drive as an additional drive to it. This means that you'll have your old drive that your computer will boot Windows from, and then the new second drive that will hold all of your additional data.
This is the easiest set-up, since you're simply adding a new drive on top of an already functioning one. All of your programs, data, and Windows functions will not be changed since we haven't changed the old drive. Just slap in the new hardware and run Disk Management to format the drive (thus turning raw storage space into storage space Windows can allocate data to), and you're done.
The only time you would need to reload Windows is if you wanted to have Windows on your new drive instead of your old drive. I would suggest this if there's a definitive speed boost between your old drive and your new drive; if you do find that you can upgrade performance by using SATA III with a new drive, I would put my OS on that drive. It's more inconvenient, but you'll get performance boosts in the long run.
That's a bit more of a complicated process, and I don't think that's what you want to do, so I'll just leave it at that.