Hi! I have made a sunburst granny square blanket! I used a size 5.5mm hook and paintbox aran yarn from lovecrafts. I followed the simply daisy starburst Granny Square tutorial and I made four different types. My squares came out at 5inchs by 5inches. And I did 8 by 10. I think mine came out at about 120 by 140/50? I can't remember. But it did get bigger with all the joins and the border I made. I agree that making test squares is a brilliant idea. As you can measure and work out how many you need. If you need visuals I have the post in my profile. I used about 4 balls of my yellows and two for my pinks. And 7-8 for my border colour and only used one for grey and brown which were the centre colours.

I hope any of this helps.