any plain popcorn will work for the most part. smaller kernels are better, i use organic popcorn for this reason.
and if your going to spawn to bulk you dont need to be as sterile, just clean, and pasturized, it may seem like a step more and its not that far off from doing big things like a yard but a tub full of substrate will produce more and bigger fruits than just off popcorn.
as to your question, thats where experimenting comes in, right now i am doing straw cakes that are in the shape of a cigar, rolled in foil. they will be layed flat on the foil for fruiting like a cake.