The BIG lesson from actual series drogue use/experience is that the historical typical spec for the cone cloth/construction was way too light. They shred in use and tear on recovery.
Commercial people were making them from 1.5oz and 2.2 oz nylon (heavy
spinnaker cloth). That has proven way too light - unless you view it as a 'one or two time use' product. 6oz Dacron is more like an acceptable minimum. And reinforce the edges - hem or tape - yes its more sewing, sorry, you need to do it.
From what I have seen, the rodes rarely fail. 5/8" sounds on the small size for your boat to me, but I suspect it is ok for anything but the true worst case scenario. Just make sure you have a decent fair-lead off the boat to eliminate/minimize chafe.
Number of cones . . . Jordan's recommendations
work pretty well for mono's but idk whether cats would be significantly different or not. I would error toward more cones if there is a question.