Don't even consider "pulling off" any tubers! That won't work and you'll be upset.
Scroll down on this link to see how to divide dahlias. It's critical to get part of the "collar" (where the eyes will be) for every tuber. https://www.dahliabarn.com/dah...
The distance apart is different for small dahlias (short in height) than it is for the huge ones. Since yours are not labeled plant them 2 to 3' apart to be safe. Put the stake in before you plant each tuber or each clump.
Do you have any short dahlias? I'd be concerned they'd end up behind the tall ones but maybe you don't have any short ones: no worries.
I'm often faced with how many to leave together and usually judge by the amount of stems coming out of the clump. Do your best to separate them (I'll be doing the same exact thing). Otherwise, if you're faced with many stems, attached to tubers, and you plant it as one clump, you run the risk of the tubers being unable to take up nutrients and the whole clump dying.
One tuber per hole is the ideal.