Yea the vinegar test is a good way to see if it is likely to react in water, another way is to leave it in a bucket of water for a week, and see if the pH of the water changes over the week.
Paving stone is generally ok, but I would be careful about putting sharp edges in the tank as fish can hurt themselves on it.
As for cleaning stone just rinse it off with a hose, and if it comes from a location you don't trust boiling it in water, or cooking in the oven can work to sterilise it, just be caefull about using that as some stones can explode in heat.