Stinkpots typically only grow to about 4 inches and can live in a 20 gallon tank their whole life (though there's nothing wrong with a 40 gallon). You'd have to get a thermometer to see how much heat a lamp would create - though these turtles rarely bask, so I'd just get an underwater aquarium heater. I wouldn't use a filter that creates a current - stinkpots are usually found in shallow, non-moving water.

Here's a stinkpot I found in Kentucky a few days ago:

Third Eye