Crank baits/Shad Raps, how, why and when to use th

I am convinced these are affective lures and catch fish.
Yes, even I have used them and actually caught some walleyes.
Accidently because I had no clue what I was doing and what I was using. Tie a pretty one on and tose that puppy out there and start reeling.
A couple years ago, Mike/HOF went over to the Mississippi and used them successfully. It was June and the water was high and he liked the shallow water up close to shore.
We fished maybe five feet deep at the most.
I suspect the original design was to imitate a bait fish, healthy or injured.
When you go into a sporting goods department, usually the largest display are cranks/Shad Raps and of course one of the most popular is Rapala, there are others.
The isle is 20 feet long and hundreds hanging on the pegs. My eyes glaze over.
OK, what to use and buy?
We got short ones, long one, skinny one, fat ones, floaters, divers, countdowns, jointed etc., etc., etc..
Are they a seasonal bait or can you use them all year long?
Can you troll them deep and what is the best way to rig them, egg sinker on a three way, what? Or are they specifically a shallow running bait?
Is there a chart or general guide suggesting the most appropiate use, you know, match the conditions with a recommended crank?
I know the Firetiger was the rage a couple years back.
Does a guy have to have a hundred on them, or can you pick out a dozen or so and cover it?