I love these. I would use 10-12.
I like going between 6-8 reps on most exercises these days but, there is quite a bit of risk to strain your lower back doing pulls so, a little higher on reps and stop just short of failure.
Play with the bar placement at the bottom too. I like to pull from right at the knee or a bit higher so I take as much glute she ham out of the movement as possible. Just think about really crushing your back together at contraction instead of pulling up.