dynamic floating

Hello everybody,
I have a horizontal space in a theme I’m developing and wanted to fill it with widgets… I thought of putting 3 of them which will be floated to the right on the same row, but at the same time I wanted them to take the full width if there are less then 3 at the same time, is there a way of doing so?

Also, is there a way of limiting the number of widget for a single widget area??

Thanks in advance