A friend of mine put some diamond cut hydroturf on his platform last year. It's really nice, and held up well last season. I don't think they offer the customization options that seadek does though.
They don't to my knowledge. Everyone I have talked to advised using the "b" stock diamond. They have it on clearance. The edges can be routed to have a custom appearance
I went with the solid 2 color largeeee sheet. If I did the math right it has enough to do my trailer and swim platform in one sheet. Was 60 shipped. The stuff I got was thinner than expected but cushy. However as I said before I'm not sure about the solid vs textured for showing marks. Prob not a big deal but can update when I get it on the platform.