OK so I purchased a road bike at a bike shop a few months ago near my university so I could get around faster. I ended up painting my 10 speed, but couldn't figure out how to put my rear derailer back on. I think I lost a few parts because the first time I took it apart, installation of the rear derailed was a piece of cake. I was planning on modifying my 10 speed to a single speed just until I could save up to get it fixed at a local bike shop. After riding around with my bike as a single speed for a few months I'm hooked. I don't know why, but it's so much more fun with only one gear and I've found hills are actually a lot easier to ride up. I purchased some Velocity Deep V's on ebay and the rear comes with a flip flop hub. I'm not sure what kind of cog (freewheel?) I'll need. I'm planning on getting a 20t cog as my dorm is on a fairly large hill and so is the campus.

From one of the ebay pictures, it looks like the flip/flop hub I got is this one here: http://www.shopatron.com/products/pr...-XX/7455.0.1.1

Here is a link to the rims I got:
http://www.ebay.com/itm/150694078661...#ht_500wt_1413

Is there a certain cog I should get for the fixed side? I'n new to this, I really don't know.
Am I golden with one of these? http://www.bluesteelcyclery.com/prod...og-65497-1.htm

Will I need a lock ring?
From the looks of it, there is a lockring.

What kind of spacers?