I agree with Steve--a solid drawing foundation is recommended beforehand. It will help you construct your subject correctly and understand the form and lighting used when painting. If portraits are your objective, I highly recommend going through the portrait course, as it covers all the fundamentals to get you started: https://www.proko.com/s/1cX2 I suggest practicing the structure of the head and then trying out rendered pencil/charcoal portraits, which will help in the transition to painting. Now when learning a new painting technique, I recommend starting out monochrome. The popular options are black, burnt umber, or burnt sienna for practice. Working monochrome not only helps you get familiar with a new technique without the overwhelming pressure of color, but also helps you develop your understanding and control of values, just like a rendered pencil/charcoal drawing. I think that is currently the main issue you are facing with your painting currently, where there is little clarity in values and structure, so practicing this will definitely help. I don't think you are too far off though, so with some effort and practice you'll there in no time :)

You need to begin with drawing. If you want to do realistic portraits, it starts with good, solid drawing. Then you can focus on the painting part. One thing I will say, is that if you plan on doing many layers of acrylic paint, I wouldn't so it on paper.