Yes, it is indeed a good start. My plan was similar only using the 3 points as the parameter.
I believe the endpoint of all fillets is @ perpendicular to the arc center point. Therefore you can determine the center and radius.
As Lee did, the simplest would be to use 1/2 the straight segment distance as the default.
If I were to get really overboard, You could compare all of the straight segment lengths, looking for the shortest, and then itenrate through adjacent segments to fine there max lengths, until all segments were calculated
Thanks! -David