holdTime = .85; //time to hold each position (seconds)
seed = Math.floor(time/holdTime);
seedRandom (seed, true);
rnd = random(39);
thisComp.layer(rnd+1).position

the random(39) line means "pick a layer between 0 and 39, which are my tracker layers. Of course, there is no layer 0, so you see lower there is a +1 to make it between 1 and 40

Nice!
What expression did you make the little text labels?

I put an expression in the Source Text of a text layer that uses the text layers position as its value:

"[" + Math.round(transform.position[0]) + "," + Math.round(transform.position[1]) + "]"

Anything in the quotes is rendered as-is, then you use the + to add more text. The Math.round part is just taking the x and y positions and rounding them so there aren't any decimals.

So if you were to read this out loud it would say "Bracket plus x position plus comma plus y position plus end bracket"

one thing I want to try is adding the inertial bounce expression, so when they snap into the new position, they'd bounce. it would be really easy and I think cool.