Regarding contours plots, it is possible to set ncontours if we want to specify how many levels we want. But when we projects contours on a 3D surface, this option is not available.
Is there any trick to handle this in an other way ?
You’re correct. This option isn’t available at this time.
I just made it an official feature request: https://github.com/plotly/plotly.js/issues/485.
Please subscribe to the ticket for the latest development info.