Nice Stack Silvia, you can determine the number of images needed using some extreme macro calculators on the web (
https://www.fotomacro.cl/calculadora/) and learn a lot on this wonderful hobby in
http://extreme-macro.co.uk/. I can suggest trying to improve the light (yes, the light is everything in photography), diffusing it as much as you can, testing different materials, such as paper, foam, in my case I started using continuous LED lights and exposure times between 1/3 and 2-3 seconds, with a manual micrometric rail. Then I bought an automated rail (wemacro) and started to have vibration problems that I solved using 2 cheap flashes (yongnuo) triggered remotely from the camera, using 1/125 sec as standard speed in most cases. That solved the vibration problem. I put difussers on teach flash and also use a foam cup in front of the optics, so I can have good light diffusion. Hope this help, have patience and practice a lot, test different settings, lights, backgrounds, and also stacking software (for me is Helicon Focus). HTH, cheers.