Thank you very much for your comments.
About the ficus leaves, I just cut them to size for what you need (coconut, banana, or other plants), and let aside for about 24 hours, so the leaves get the "right" form, curving down and getting the look of real leaves.
When I see that the form is allright, I just paint the leaves with a generous coat of acrilic paint (I use Vallejo aerografic acrilic paint), and make the "effects" I need (drybrushing, washing, and so ...) I only use acrilics, so I donīt know about the effects of enamel or oil paints on the leaves ...
I have some leaves painted this way two year ago, and no problem ... looks like the first day ...
Best regards.