If you want to add alcohol you need a way for CO2 to escape, you should have done that in primary anyway. Secondary is a clearing tank. By that time it should be done fermenting and time to get the yeast and proteins out of the beer.
How long depends on what you want to do. If you want to age it just leave it a 70. If you just want to clear it put it in the fridge. Clearing could take two weeks, if you add gelatin it will take only a few days.
You could add some sugar to help carbonate it. If it's in the fridge you will have to connect the gas line to carbonate.
