AJ, My rear track wheels are fixed on both sides but have threads for both a cog and a lock ring on both sides. So when I regear a bike, I typically flip the rear wheel from a 15 to a 14. If you are going to get an axle that has a free wheel on one side and a fixed on the ohter, that is okay too. Make sure you get a very good Park Tool rear cog chain wip to remove the cogs and lock rings. The cheaper ones do not have enough leverage to get the cog off and if it slips, you knuckles get skinned. It is incredible but I have several hundred dollars in chainrings, cogs and tools for the fixed gear bikes.
Also, watch which handlebar is provided with the fixed gear bike. Many times the bike is supplied with sprint bars. These bars have a deeper drop for sprinters who basically go around the track 3 times and sprint for the last 200 meters. There are endurance track bars that have a shorter radius and less drop.