Minimum numbers of colors for a good detailed image ?

Hello !

My name is Alex and I write to you from Canada. I have been really enjoying reading about your process ! It seems very easy and understandable except a few pointers I wanted your help to understand

I have been trying to convert and prepare an image just like you have demonstrated on your Website and I would be using a Projector to mark my lines on the canvas

However my goal at the tracing stage is to have an many minimum lines and colors possible to make the best detail (something like 8-9 colors) because anything less than this makes the image too weak and anything more than this , results in a chaotic mess of numerous lines on the canvas
while tracing !!!!!!!!!

I know in your tutorial , 25 - 30 colors will definitely produce a good detailed image but what if someone was to start with 8-9 colors but good detail ?

I am looking at a realistic portrait style

I donot wish to paint directly while projecting as I donot have a permanent projector with me at this moment and is borrowed

Please help !!

Can you also please do a quick image tutorial if possible in which an image can be converted in the least numbers of colors but best detail possible ??
I am a beginner and I really want to try out this method because this looks very very promising !!

Thanks !