That's (post #4) right.
You will find differences in the smallest increment to which a servo will respond. Many years ago, there was a study that showed definite differences in that "accuracy" between the popular manufacturers at the time (Futaba, Hitech, Airtronics, and JR). Unfortunately, that specification is rarely, if ever, listed. Coreless and/or digital servos may be better in responding to smaller increments. I don't think I would depend on the specification speed for tight control. When modelers gang multiple servos for large models, they try to match them.
What you want to do is so vague at this point that it is hard to give specific advice. Unless there are specific and different needs for the different servos (such as max speed, torque, shaft wobble, handling shock loads, etc.), I would get a bunch of identical, general purpose servos. You can get modern servos for about $25 each that are quite good. Even the $10 class of servos work fine. You can also go up to $200 servos, which is probably overkill.
John