I've already tamped the 3/4 minus and 1/4 minus bed. I'm now ready to lay the stones but have been reading a lot of conflicting opinions on the material to use.

Special considerations: I'm using thick slabs of granite and marble discards pulled out of dumpsters at local countertop cutting shops. I break them smaller pieces to look make them look more natural, 1-2 sq feet or smaller. So, having laid flagstones a long time ago, this should be much easier as the surface and underside of the stones is flat, making leveling much less tedios. I'm not sure if I should put a layer of material under the stones or just lay them directly on tamped 1/4 minus surface and worry about filling the gaps between the slabs.

Concerns: Drainage. This is a low spot on a two-tiered yard and anything that considerably inhibits drainage could cause a temporary pond as the water has to go straight down as there's no where else to go. The tamped gravel bed is draining pretty wall, as is. I'm in Portland, Oregon so rain is frequent but no "flash floods" usually.

Sand: good drainage, but I'm worried about ants. We already have an ant problem in the summer and I figure they'd love the sand option.

Polymeric sand: From what I read it inhibits drainage considerably. Also, not crazy about acrylic/plastic in my yard

1/4 minus: One local landscaper suggested this and the only downside I can think of is the gravel would end up on the slabs themselves and I might be constantly sweeping it back into the cracks.

Rock dust/screening: One opinion I read is that it inhibits drainage. Also, not sure where I can find it out here. I've already called a couple of landscaping outfits and they weren't sure where I could find it.

Soil: Moss grows very very easily out here. It would look great to have moss between the slabs, but I'm not sure what the downside would be. Weeds? Chunks of moss breaking off with foot traffic?

I may be overthinking this option but would appreciate someone with experience to share their opinions.