Weather-wise I would be looking more at icing picked up at a higher altitude, I don't know anything about the Phenom de-icing capability, but the plane can't be that old. The NTSB said they have the full data recorders and they look like they are in good shape. Those are already at the DC office and I am sure they will be working the boxes throughout the night.
2500 is not very high for the ceiling. From Manassas is a short run, but I would be interested to know from what altitude they began their descent into GAI. The airport is small and not easy to find in the residential clutter around it, but that shouldn’t be a factor with good nav eqipment.