One Piece Shower Need Help Recaulking One Piece Shower?

Need help recaulking one piece shower? - one piece shower

The walls of my bathroom have fallen. I have a piece fiberglass shower / tub in the assembly. I am preparing to paint on the toilet and remove the seal cracks around the shower. There are nearly one quarter inch difference between the top of the shower and the sheet rock. Now I only fill with thick or do I make a difference smaller than Spackeler putty. I also paint the first room, then paint or sealant caulk first and second place.