Given that Schubertiades took place with audiences anywhere from a few to a hundred, we have to assume that the physical spaces for dancing varied greatly, too. In a small space -- a drawing room of one of his friends' apartments -- the piano would probably be small, too, square. Chair with a back, not a modern-style piano bench. The piano positioned either along a side wall or, if there is space, angled out into the room (as in Kupelwieser's watercolor). The amount of resonance in the room would vary greatly, depending on wall coverings and the number of people, but would probably be fairly high since the floors would not be carpeted (or any carpets would be drawn back for the dancing).
Schubert playing, looking occasionally to the side at the dancers, especially the Vortänzer (the lead couple), and listening in case the Vortänzer call for a different figure, dance, or a pause (common in longer dance sessions), during which Schubert might continue to play or might stop, too. Persons not dancing, male or female, sitting or standing close by, occasionally talking to one another or even making brief comments to Schubert on his improvisations or requests to hear familiar dances. The distinct timbres of the three main registers on contemporary pianofortes would be audible nearby, less so on the dance floor, where the swishing of clothes and muffled swish-slide of light cloth dancing shoes would mingle with the music. The shapes of the dancing would have varied, from couples dancing freely within the dance space, couples moving in a "round dance" format (around the room along a line of dance) to chain dances or even something like the "parlor game" formats of the quadrille. Windows closed, perhaps shuttered against the night.
In breaks, food and perhaps the light, young Austrian white wines of which Schubert was said to be particularly fond. He was a "lively" drunk, and it would probably have been difficult to get him to return to the piano late in the evening if he had had too much. These, among others, were the occasions when his duet-partner, Josef von Gahy, would take over to play for any dancing done in the late night hours.
In larger spaces, Schubert would probably have had a correspondingly louder wing-shaped pianoforte to play, and the temptation to move back and forth between music for dancing and dance-music performances would have been that much greater, as well.
Note: In Kupelwieser's watercolor, the pianoforte appears to be a small spinet -- thus, neither the square piano one might expect in that space nor the larger instrument one sees in the Schubertiade drawings and other graphics.
