A barn that size should hold around 500 head depending on ventilation. That's way more management than you're going to want on your first run. I agree with the others- pen off a small section of the barn and do just a few to see how you like it. In order to be efficient, unless your are running Holsteins on self feeders you really need a mixer-a large investment.

Be prepared to buy or use a lot of your own corn. You can only use dried distillers for up to 20% of your grain ration depending depending on the amount of sulfur you have in your water. Wet cake or modified wet cake will allow for more. If you fill it be prepared to clean pens once every two weeks when the cattle come in and at least once a week as they are nearing finishing.

Using buildings for confinement (monoslope preferred because of sunlght and ventilation) is a VERY efficient way to feed cattle but requires a LOT of management. Guys up here are getting well over 4 lbs/day of gain (close to 5 in some cases) in confinements.