There's not a great way to estimate the afterburn. It's not going to be huge numbers, so I would just consider that a bonus to your daily/weekly goals.
For bodyweight exercises, I would leave the "weight" field blank.
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everybody on the couch."