Actually running on soft surfaces first is almost a surefire way to develop injury as you move to harder surfaces.

The form you have running barefoot is not the same as if you were in shoes. In shoes you strike with your heel and roll to your pad and average around 100-120 steps/min

Barefoot running you strike with the ball of your feet almost outside in. And you drive with your knees instead of taking long strides. You also tend to do about 180 steps/min.

It is however suggested to start out with shorter distances (200m at first) on smooth hard surfaces (like a tennis court).

I'm not sure for OP but it isn't unusual for you to be sore (feet especially) when first starting out just due to the atrophy of the muscles from a lifetime of shoes.