The depth of the foundation should be beep enough to properly embed the anchor bolts. This would vary based on the size of the equipment. First, consider the mass required for the foundation. Next, consider the 30 degree rule for a stable footprint.
Remove all laitance with a chipping hammer.
Make sure the concrete is properly hydrated.
Be sure the concrete is free of any oil or contaminants.
It should be big enough as to not violate the 30-degree rule.
It is recommended that expansion joints be installed every 4 to 6 feet.
Make sure the top of the expansion joint is sealed with an expansion joint material, elastic epoxy seam sealant or silicone caulk capable of expanding.
After the grout is cured, remove about a half inch of the expansion joint material and seal the top with an elastic epoxy seam sealant such as Chockfast Expansion Joint material.
The number of anchor bolts is determined but the equipment manufacturer.