1) - This is a new snake, and you should be practicing quarantine. If you take the mouse and give it to your corn, that would be violating quarantine. If you are really worried about wasting the mouse, you could re-freeze it, as long as you keep it separate so you know it can only go to your new snake. I think my choice would be to leave it overnight and see what happens.

2) - The most common recommendation when new snakes don't eat seems to be to wait 5 days then try again.

3) - You could try f/t again. Most people recommend to feed a new snake whatever it was getting at its old home until it is settled. So give it live until the snake is settled and you've got a few successful feedings. When we first got out snake, she was used to live. We tried 1 f/t, which she refused. We gave her live a few times, 3 I think, and then tried f/t again. She took the f/t then and has never refused a feeding since.

4) - Yes, you probably scared him by taking him out of his hide. He is still getting used to his new home. Especially if he is a baby; they get frightened more easily. You will probably have better success if you feed at a time when he is active anyway (late evening) so you won't have to worry about removing him from his hide. Also, pre-scent to get him in the mood to eat.