First off, you can FMQ with a Singer 66, but that isn't the best vintage Singer machines to FMQ with. The Singer 15s (15-89,15-90,15-91) are the better choice since the bobbin (rotary) is situated in such a way that the thread picks up in a manner more beneficial to FM.
A Schmetz Univeral 90/14 should work for needle. I use cotton thread, like Coats and Clark.
I have found that if I have spray basted the quilt, I will always get skipped stitches. So, I no longer spray baste; plus, that stuff is nasty on the lungs.
You have your darning foot on, but I don't see a layer of material and batting for your stippling practice.
You need to practice with all the layers.
All I can suggest is for you to continue to practice and follow any suggestions that Leah Day has put out there.
Each machine is different, so you will have to play with the machine. Looks like your machine has a motor. So, practice with the speed to see what develops.