The spinner will hold two people sitting on its platform, and be able to support two more people climbing on top of them. So 4 people * 250 lbs = 1,000 lbs.

We also need to know the dynamic and thrust loads in order to source the bearings that will take the force of all of these people pulling on the shaft. 

Dynamic load refers to a force on a system because it is accelerating an object in a given direction. So that's the people sitting on the platform, and it is not moving in the vertical direction.

However, there are dynamic forces in the horizontal directions. The horizontal dynamic load is a wheel turning at 60 mph (that would be crazy, but it's a high estimate) and going from 0 to 60 in 20 seconds.

Rate of acceleration: 60 mph = 88 ft/sec, divided by 20 sec = yielding 4.4 ft/sec^2.

Force = mass * 4.4 = (200lbs (platform) +1000 (people)) * 4.4 = 5280 lbs.

These are ridiculously high estimates. I think spinning at 60 mph might make people puke.

Thrust load runs parallel to the axis of rotation.