what is the least amount of play a DS should have before it bottoms out? at ride height a have 5/8 inch

3/4-1" is optimal

Giant numbers like 1 inch are used to cover all applications but type of suspension and wheel travel will change that number slightly.

A lowered road course type car with short shocks and stiff springs will require very little yoke clearance.

A lifted truck with long shocks will be on the breaking edge at 1"

With that said. Without bottoming the yoke out, less is better. It makes for a more stable driveshaft and high driveshaft rpm.

Most cars barely use up 1/4" of travel.

It really depends on how much spline length you have in the tranny yoke, if there is 3.0 inches of spines inside the yoke then 3/4 inch sticking out from pushed all the way into the tranny with the car resting on the suspension with a full tank of gas and simulated driver and passenger weight in the car would be good in my book. If the tranny yoke had 4.0 inches of spline inside then 1.0 inches sticking out would work for me with the above conditions met

You're OK (barely!). On a problem app a person can space the front shackle(s) of the rear springs rearward a bit (keep an eye on rear vertical shackle angle) and or shift the eng/trans forward a bit