Don't judge your fermentation by the bubbling of your airlock. I've had beers ferment without any airlock activity whatsoever. Just take a gravity reading in a week or so.
As far as adding extract post boil, I wouldn't worry about it. Extract is concentrated enough that it's tough for it to carry bacteria. Plus, if you added it prior to cooling your wort, it probably got sanitized. Any temp over 180 degrees is hot enough to kill bacteria.
Relax. Don't worry. Have a home brew.
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