I think you will be ok, the continuos foam is the best solution, but you go with what will work for you. You only need 1-1/2 of bearing for joists anyway. You could cut the 2x4s in half and reduce the footprint.
Make sure you run the foam up the side wall also, any exposed concrete or blocks have less than 1 r-value.
Just extend the plywood over the foam areas, your going to be fine.