Sorry if this one was there and I missed it:
"Pull the trigger" = actually do something you've been contemplating/ planning for a while
I always understood a "shotgun house" to be one designed in such a way as to minimize street frontage and thereby minimize property taxes, an 18th or early 19thC term. Houses built to accomplish this were one room wide and 4-6 rooms deep, with doorways aligned in the same spot in every room. It was said you could open the front door, the back door, all the interior doors then fire a shotgun from the street to the back porch without hit anything in the house.