I want to purchase and try some Rapala and Bill Norman crankbaits. My question is what sizes or running depths should I try first. Rapala of course makes the DT series in at least five sizes:

DT04

DT06

DT10

DT14

DT16

Norman also comes in various sizes as well:

Little N 4'-6'

Middle N 6'-8'

Deep LN 10'-12'

DD 14 12'-14'

DD 22 15'-18'

Of course I cannot afford all sizes for now, but I wanted to buy at least 2-3 sizes in about 2 different colors. What would you recommend?

This is a very super duper general question you ask however imo,,,,

how about the 04, 10, 16 in a bream color, shad color and craw color and remember crankbaits are better when you thump the grass r timber etc good luck

Shouldn't you be answering your question about running depth since only you know what depths you want to fish?

As to colors, I'm not big on them as an ultra-important factor. I generally get by with two colors, something muted like shad or bluegill pattern and something louder, usually firetiger.