You can get the width (in points) using: selection.Cells(1).Width

You can get the vertical position of the top of the cell using:
selection.Cells(1).Range.Information(wdVerticalPositionRelativeToPage)

There's no direct way to get the height of a cell. There is a Height
property, but that reports the row height setting; which usually doesn't
help. You can calculate the height by getting the vertical position of the
beginning and end of the cell range and subtracting (and checking that the
cell is not split across pages).