Dumbbells especially adjustable ones do not take a lot of space and they are not only for the upper body muscles. Squats with dumbbells especially bolgarian ones is a good way to get muscles on legs and it is enough to do it once a week as long as weights are heavy enough so you cannot do more than 8-12 repetitions. But I would advise to pay an instructor for first few times to get the proper technique to avoid mistakes leading to injuries.