The 1 x 4s under the 5/8" may wind up walking and talking.
As long as you are going super heavy duty please consider ripping some 3/4' birch-maple 3 1/2" tall for your 16" centers. Those 1x4 sticks of dimensional lumber strike me as your Achilles heel.
In keeping with your battleship build I would go with Advantech decking. Smooth, flat, unable to absorb moisture. $30.?? per sheet, 84 lumber.
Being wall bound on at least two sides working on this pike will be a young man's task.
The 8" joists combined with the 4" cross members with be a significant obstacle when working from underneath, a 12" reach up! Might bite you down the road.
If you are going to stay with the 8" joists you may want to bridge them to restrain their natural movement over time.
I did have a friend with an 9' platform which was very awkward to work on so I cut a river up the center so he could walk in.
