The important thing to remember is to take it very easy.
My first experience with "Barefooting" was a very short jog of no more than 50 metres.
You have to think of how you are running ie:up right posture, land on the ball of the foot...slowly, slowly.
The next day you may well feel your calves, its not aching as such more a feeling that they have been working.
Have a few days off from "barefooting" then try again. Dont expect to be running distances for some time.
Im now at the stage where I will run( similar pace to when i have shoes) approx 2 miles on grass, paths. Its not rocky but there are stones, twigs, sheep s*** & deer poo.
For my fell runs I will use the X-Talon minus the footbed or if I want a minimalist "Trail" run Im now using the Roclite 285 again minus footbed.
I also use a minimalist shoe (F-Lite230) for my everyday work shoe so that my feet, calves etc are getting use to working and strengthening.
There's nothing like "barefooting" in the rain on grass