Building narrow deck

I'm building a deck on the side of my house. it will only be 4'6" wide. I'm going to make it a floating deck and use those Deck Blocks. My question is, in that 4'6" width, how many blocks/joist do i need? I was thinking 2 or maybe 3 at most since it is so narrow. I plan to run the joist long way, and then place the decking boards across the 4'6" width. Any suggestions? The deck will be narrow, but about 50' long.