Yes you can walk around and come back and there are more. Im my experience you have a better chance of finding pokemon by pokestops. So it's best to walk back and forth betweem pokestops, you will find the most that way. However if you want to find a variety of pokemon i feel it's better to walk to different areas.
Also when you get to a higher level you will get lures, or you can buy them. You can place those at pokestops and the pokemon will come to you. I found the best way to level is use a lure at a poke stop, use inscence (which also attracts pokemon to you), and a lucky egg to double your xp.