Don't boil the hops. Hops are sanitary coming out of the bag. Don't drop them on the floor before putting them in the fermenter....... but I've never had anything get infected from dry hopping.
They will sink with or without cold crashing. I do 5 day pellet dry hop additions (meaning 5 days prior to bottling) and they sink. There may some little hop floaties but they're noting to worry about.....
I have cold crashed 2 or 3 beers and didn't notice much difference so I haven't cold crashed since.
Up next: Kolsch, Alpha Squirrel, Tripel rebrew, Witbier
Currently Fermenting: Charlie Sheen (barleywine)
Kegged: Tiger Blood IPA, Irish Red, Strict Observance Tripel
Bottled: Dry Stout, Pliny the ..... Squirrel?, Cream Ale