You've come to a great place to find competent buyer agents. Look around the site and get a feel for agents through their Q&As and blogs. Yes, you can definitely have more than one agent. It's a great way for you to cover a lot of territory. Some of the more insecure agents may ask for an exclusivity with you for a period of time, but good agents will earn their keep without a contract locking you in.
You should look for agents with the SFR designation if you need one who specializes in foreclosures and short sales. You can check on our site for more info or look for it on the web.
As for renting a property before you buy, it can work for regular sales, but it definitely gets tricky if you're in a foreclosure or short sale property. In those situations, the banks have the final say on how and when the property changes hands and you may be forced to move with little notice.