I am curious how much damp proofing is recommended for a perimeter foundation around a slab that is poured about 20 inches above pre-existing grade. I am building in an area with a high water table (12″ down) so we excavated down about 20 inches to sand across the whole building site and beyond the foundation by 2-3 meters and then levelled out the hole with 10 – 16″ of 3″ rock. The footings were placed on top of the rock and then 20″ foundation walls. I plan to put 3″ of foil faced EPS insulation against the outside of foundation, then backfill with drainrock covered in filter fabric and sand. From last winter it appears that the water table may reach the footing level without drainage so we are putting in a trench daylighting to a ditch and filled with drain rock wrapped in filter cloth and a 6″ pipe inside. The bottom of the excavation to the bottom of the ditch drops 2′ (less when ditch is full).
I imagine that perforated pipe around the whole footing perimeter might not do that much extra – I would feed about 20′ of 4″ perforated pipe from each direction into the 6″ pipe and also two 4″ rain water pipes. The main house and suite cover an area about 100′ x 24′. I think I will put filter cloth down and fill foundation box with pit run gravel, then a layer of screenings for plumbing. Would another layer of 3/4 crushed rock be needed to stop capillary wicking or would 2 layers of foil faced EPS or regular XPS and plastic be adequate under a slab? Should I use paint on waterproofing around perimeter under foam insulation? We are using a double layer of sill gasket under the stud wall.

Thanks for any advice.