We would put a 24x24x3.5 cottage pad down on the concrete, build up your height with cinder block, cut the last block to the height you want, then fill in the blocks with concrete mix. paverdeck.
I would use PVC decking over composite or wood - it is a better investment. Whenever you have natural fibers in decking, you are sure to have decay, staining and other problems. To find out if a product is supported by the manufacturer - read the warranty.