You can have more than 1 barracks! I suggest at least 10 barracks per town. As a new player you can usually run 10 barracks and 10 cottages. More advanced players can sometimes run towns with 14-16 barracks!
I see a lot of new players with only a few barracks. It is impossible for them to keep up with me if they can only make troops 1/4 as fast as I do.
A good strategy for your first Evony city is to build 10 cottages, 10 barracks, and one of every other structure. Since you’ll be destroying your warehouse after you build your forge you should be able to build 1 of every building and still have 10 cottages and 10 barracks.
10 cottages allows you to have a good sized population.
10 barracks allows you to train troops faster than the newbies that only have 3 or 4 barracks.
I destroy the warehouse because it is useless unless you have a bunch of them and it is more valuable to have barracks and cottages than a warehouse. For more information see the advanced guide.