I have always put my rats, mice and rabbits in a bucket of hot water, no zip lock bag, and let them sit until the water is cold, then dump it out and fill it again with hot water to make sure the guts are warmed up. Every snake has always eaten for me, and I feel it goes down easier when the rodent is wet, rather than dry fur.
This is just how I have always done it, I don't weigh my food, I just buy whatever sizes I need and feed them, I don't worry about what exact temp the rat is, if it's warm, it's ready, none ever have refused a feeding in the 22 years I've been keeping constrictors. Other guys like to make a science out it, that's cool, I just have never been into doing it that way. You're on the right track, and asking good questions, but some of it is a learning experience; get to know your snake and the signs he is showing you, and have fun with him.