This is a really great set of drawings! You're really good at constructing the form out of the lines and circles. For your question, I recommend drawing from a reference and then using your drawing as a reference to copy it, then weaning yourself off from there. Or you can always use references, whichever you prefer. There's no rule that says you can't
I think these are really nice esp for someone who's new to these. My one critique is that the ones in the beginning have a better fluidity to them than the stiffness of some of the later ones-- try to carry over the looseness from the beginning into the final form
