Thread breaking - usually tension problem, sometimes a barb on the needle (even if it is a new one!), occasionally it is a bad batch of thread, and, as someone else said, some machines like some threads better than others.
Top Tension: I get mine adjusted by turning the tension knob to the lowest setting. Then I start sewing a few inches at a time, check the stitches front and back. If the back stitching is loose, I turn the tension knob a half turn, repeat the process. I do that until I have satisfactory tension on the top and bottom.
Bottom tension - there are you tube videos that will show you how to set the bottom tension. They are correct!
My sister had a problem on her small arm with thread breakage so she and I went through all the steps for setting tension, got it right, but the thread still broke. Then we checked the needle...sure enough, there was a barb. Next time, I'll start checking with the needle!
I use a pc-quilter with my HQ16, so can't offer any advice on free motion quilting.