Hi Nina,
The smallest diamond we sell in this setting is 0.25cts. The widths of all our engagement ring bands is approximately 3mm and the height of the diamond is approximately 3mm.
The answer to the Petra questions is exactly the same as above....
By the way these are our 2 most popular engagement rings, fantastic rings that we make from scratch once you place your order. It usually takes us 7 - 10 days to get the rings ready for you.