my answers and this doesnt mean that they are 100% correct its just how i do things. Im guessing you have a small collection.
question 1

I have never noticed any smell from my rats. I defrost them in warm water in a bag in an old pot. This can take some time depending on water temp and size of pray. Don't make the water to hot you don't wanna start cooking them. When their defrosted I use a hair dryer to heat them up, paying most of the attention to the head ( thats where there gonna strike).
Defrosting them in you room is a good idea. It sents the room and can make them more likly to eat.

question 2

Again never had a smell. always defrost in a bag. 9 outa 10 times the snake isn't gona eat a wet rat.

question 3

most pet shops should have them. If your looking to buy in bulk online try Rodent Pro.com

question 4

I have never order rats online because I have a reptile store 5 min from my house. From what I have read on feeder sites they are shiped over nite (expensive) with ice packs/dry ice.

Before you go and put in an order some where get some frozen and see if your snake(s) will eat them. Getting them to switch can be very hard. I got 2 that just wont touch f/t or p/k but will hammer live. some switch with no poblem so if they don't take one right away keep trying.

I hope I helped you out a little