The dimensions of the plate on the Everbilt 5 in. Red TPU Heavy-Duty Swivel Plate Caster with Brake, 330 lbs. Weight Capacity is 2.85 inches L x 2.52 inches W.
You have to buy them Individually.
The holes are at the 4 corners of the plate. For a detailed spec with dimensions you should reach out to Customer Care and they can put you in touch with the manufacturer.
The plate attachment has a 5/16 in. screw hole.
I believe the weight for the wheel is 330lbs.
4 5" hex nuts per wheel.
This has a working load limit of 330 lbs. per caster.
There is oil in the ball bearing, so lithium based grease is not needed. If you feel it needs more oil it can be added and will not hurt the caster.
The total height of this caster is 153 mm (about 6.02 in.).
Haven't done that, but based on how I've seen them perform and their build, I would say probably not great if the sand is any deeper than 1" thick or so.