Unless you are buying a replica cowboy revolver like a colt SA, or an old (30+ years) you should not have to worry about leaving the chamber under the hammer empty. Be sure when you do purchase a revolver to throughly read the owners manual, which will advise you to the correct operation of the revolver. Also the place where you purchase said revolver should be able to give you advice in this area.
If you are getting the gun for self defense, a 4 inch smith or ruger in 357 will suit you fine. If a more compact package is required you may go with a hammerless smith in 357 or 38. I would stick with the 357 because of the increase in power for self defense, and you can practice with the lighter 38 special loads. Go to a gun shop and ask for their help, handle several guns, then go back home and look up all the info you can find on the internet about the revolver you like. If there is anything negative to be said about the revolver, it won't take you long to find it online. If you stick with a S&W or Ruger you should have no problems.
Make sure once you have purchased to spend allot of time on the range. Learn the safe handling of your gun, put several hundred rounds of practice ammo through it and a box or so of the load you will be carrying in it. You want to know where your bullets will strike in reference to your sights at different ranges, and ensure your ammo of choice functions properly in your firearm. At home, make sure your gun is unloaded, (triple check, then check again, I leave ammo in a differnt room) and practice your draw from holster, dry fire in a safe direction to learn trigger control, and just like anything else the more you handle your gun, the safer and more effective in its operation you will become. Just remember Safety, Safety, Safety, Guns are not toys, don't aim at anything you would not want to destroy. Good luck, and hopefully all you'll ever have to shoot is paper and pop cans.