Should be sufficient if you have micro fauna. I really would not worry if it gets on the glass espeically if you just added the star, but one way or the other you'll know about 8 to 10 months down the road if you start to see its arms tips starting to atrophy off. As long as they have sufficient sand bed to cruise on and micro fauna to eat and the sg and ph is not out of wack they do just fine.
I have been keeping a typcial star that is ofund in florida waters for over 3 years now and its doing great. It was only about 1" across when I found it, and its now approx 3 inches across. IIRC the locals here call it a grass star......similar to a typical sand sifting star but mnore orange with short knobby tops similar to a bahama star, but not as high of a center section and the arms are rounded with no flat spots. They are very common in the Gulf of Mexico.