how many fills does a size 10 band need for good restriction? does anyone know?

If by "size 10" you mean the VG band with a 10cc capacity, the answer is the same as with the 4cc band. The number of fills any one person needs for good restriction is...the number of fills that person needs for good restriction.

I know that's not much help, but it is the answer. With the larger band the size of each fill is going to be larger, but the dynamic is the same. The first fill probably won't result in a significant increase of restriction, while fills # 2, 3, 4 and beyond probably will result in restriction. As you lose weight, your restriction will decrease and another fill (or, more properly, "adjustment") will be needed.

Everyone's experience is different. So there really is no answer to your question.

I have the VG 10ml band and have had 9 fills and have 9.6mls in my band now. I have good restriction with 8.9mls for a couple of months and lost 15 kgs or so and the restriction gradually went over a period of a month or so. My friend has great restriction with 4mls in the 10ml band. It is never the same for 2 ppl.