I have printed too the IE version at 100% scale, my tube are stainless steel and have an perfect 25mm. All the 608 bearing of the roller are in contact with the tube. I now building the Z axis and some of the bearing at first do not touch the tube, to solve this i simply removed some pla that make the curve that not allow the bearing to touch the pla. removing some of the pla put the bearing a little more inside. Some bearing have an little play in the 8mm screw, when you screw the M8 you can make some pressure to the bearing to have the bearing more inside.
i have checked your roller play video and this will not be an problem when the stepper motor have electricity.
When the motor is running it not allow to pulley to move and remove all the play you have. I do not have checked the marlin firmware given my Vicious, but you need to configure the firmware to allays put electricity on all motor. by default when an motor is not used for some time, the electricity is cut and this can be an big problem.
About your circle problem, this can be related with missing steps.
you need to check if you steppers have enough voltage to not skip any steeps, what voltage you have on each steppers?
Other thing is important, for your first tests i think is more easy to find the cause of this problem if you make circle using an pen. The pen will not have any lateral force and pretty sure it will not miss any steps. If the circle drawing is perfect, then is very likely is an voltage problem.
Check too if you have some play on the z piece.
Are you sure your cnc has all corner with an perfect 90 degree? an easy way is to measure both diagonals, if both diagonal have the same dimension, then you have an perfect square or rectangle. But i pretty sure this is not your problem, to have the circle posted in the photo your cnc should be really out and this will be easy to see.