Hi Davide,
Yes, I'm not surprised that this is new to you. It is a very common mistake re the 5th Hussars. Besides Petard, please check out the late great expert Lucien Rousselot in his plate #57. Three rows of buttons for the 5th and some of the other older hussar regiments from the ancien regime. I'm surprised that 'RIGO' shows five rows. I have great respect for his work. To my knowlege, there were never four rows. Only three or five rows on the dolman and pelisse.
I have been working on a Historex conversion of a trooper of the elite company of the same regt. It has been my favorite hussar regt. since I was a little boy. I love the color combinations. By the way, before you start painting your superbe figure, we should talk about the shade of blue involved. There is some controversy as to that! If you are interested, send me a private e-mail and we shall talk about that topic. All I'll say for now is......how do you like Detaille as a source! All the best.