How to fix crack in shower tub

Has anyone removed a tub? If so what should I look out for? I may be able to gain access to the bathroom side with no problem, but the other sides one is the bench for the table the third side is the walkway and the forth side would have the piping in it and it looks to be about 3 inches thick. I just may replace the whole tub and walls and it done right. I believe the tub is plastic not fiberglass. I see no glass fiber in the brake. The real problem I see is the walls is also the ceiling too, and in it has a skylight.

Thanks

Buster