As far as the tank goes, sirens can grow up to 24 inches so get at least 3 times their length as the size of the tank.
They live in shallow water so you don't need to fill the entire tank.
Temperature isn't that important as they are used to living in shallow pools of water.
Get the finest gravel you can get because they like to burrow. Ideally you would have mud but that's probably not an option.
Get enough stones, plants, ... so they can hide.
Food: they eat live food. Bloodworms, tadpoles, ...
They are active at night so you will have to feed them shortly before your lights go out.
Keep in mind that males can get very aggressive around spring. They will bite whatever they can get hold of.
Don't keep these with fish and remember that they can live for as long as 14 years.