Okay, I'm a little bored so.... *ding, ding*

-Panniers are those bags (what you called "side pouches") that hang on the side of either a front or rear rack. Most opt for the rear. The price will vary according to quality and attachment system.
-Rack trunk or trunk bag are those soft sided bags that mount to the top of a rear rack. Some of these have fold down mini-panniers, some have a bellows that allow for the main compartment to expand up, some will do both, and others won't expand at all. Some will feature some kind of Quick Release system, but you have to match the brand of bag to the rack. Topeak bag works with Topeak rack, but not an Avenir rack.
-Seat post racks attach to you guessed it, the seat post. Mixed reviews on their design, but most will agree that for your application, you shouldn't even consider one.
-Heel Strike is when the backs of your feet hit the panniers when you pedal. The bike's geometry plays a major factor in how you will carry your load.

Then you get to the rear rack itself. Their design will vary by their intended purpose. Some work best with just panniers, some with trunk bags, some can do either one, and others can do both at once.

As far as the best place to figure out the different designs, visit Amazon.

Most people will recommend you go with a rack and pannier for your load. You might get more helpful advice if you could state a budget, either ball park or hard limit, as well as make/model of your bike.