I think the average is 1 unit of insulin to 10g of carbs. That is what DAFNE teaches and work to. Obviously there will be differences but 1:10 is certainly a good starting point.
Yes, 1:10 is a good start point. I'm currently using 1.1:10 as some extra drugs I'm currently having have moved my blood sugar up a bit but I was around 1:10 before that