1) Use global variables, a variable "Day" that you set to 1 if it's day and 0 if it's night. You can have a whole bunch of variables, put them on a different event sheet if you want.
2) If the object it global it will keep it's instance variable values and appear at the position it had in the previous layout, make sure you specify in every layout where the player is supposed to spawn.
3) I recommend you read the blog articles and tutorials by Ashley on optimisation and performance.