"Did you bake it just to dry and sanitize it for storage?"
Yepper. Kill off any snails, nasties, etc. and dry it.
"Is the sand as good as Ada for plants or is it limited to its buffering ability?"
I don't know if it is as good for plants, since I'm not a plant guy really.
"If there is no ammonia leach how soon is it safe for shrimp after setup?"
Pretty darn Safe. Give it time to adjust the ph and in they can go. (Now take that with a grain of salt. What works for me, may not work for you.) This last time I let it sit three days and in the shrimp went.
Now, keep in mind to do it right you still want time for biofilm to build in your tank...