Two SSDs is definitely optimal, but not really needed. General consensus is to move the OG hard drive to where the optical drive was, and put the SSD where the hard drive was. Then put the OS/Apps on the SSD, and other data files on the HDD.
I've yet to see anyone be disappointed in the outcome. Every video or article I've seen have noted significant increases in performance.
I'd recommend shopping around as opposed to going with macsales.com though. Especially with Black Friday coming up. You'll be able to find better deals for RAM and even the bracket for the optical bay on Amazon. Newegg is also good. Slickdeals usually has a few deals per week for SSDs.
I'm actually looking to buy a mid-2010 White MacBook to do this to. Those are my favorite MacBooks ever

. Should be able to grab the laptop, max out the RAM to 16GB and add a 250GB SSD for around $300.