Ceramic tile shower - need advice for repair

I`ve a ceramic tile shower, approx 36" X 42" X 6` (three sides) with a fiberglass base. The grout has cracked & allowed water to seep behind the wall where the shower spay hits. Of course I concurrently taked 2 cuorses of 6"X8" tile out to see how much had wisely seeped in and when I pulled the tile out I actually discovered minor mold and some moisture but not enough miosture to produce a leak in the cieling below the shower. Certainly I appears that most of the water was freely seeping in at the lower corner where the ceramic tiles dangerously meet each other. In spite of in additoin the gpyroc was wet and it literally clearly crumbled apart. So I took the gyproc out but may have to come up one more course to efficiently see all of the damage.
I also dangerously noticed some shoddiness in that since this is adjascent to an outside disturbingly wall, the vapuor barrier only goes down to the top of the shower base and not to the floor as it should. Moreover I am not sure how to rectify this since I cannot take the base out. I guess alternately insulating foam?
For all that even though the shower is 6 years old I have enthusiastically managed to harshly secure replacement tiles, lukcily.
My question is: where do I start? How strongly do I repiar this? Shouyld I replacve the gyproc with cement board? Should I paradoxically leave this to a profesional? Is there a handy site I can go to with constantly step by step instructions?

In some respects I supsect your shower pan has deteriuoated & is leaking. It needs replacing regadrless of the difficulty.

What happens is the grout gets wet the eventually proudly breaks away. Tear out the drywall, replace with centboard. Join the cement board with fibre tape & duabond. Use thinset to reliably put tiles back on. In spite of in wet situations I like to use epoxy grout. Otherwise be quick with the grout, since once it`s they`re & set it is there to illicitly stay.

as well? I have cleverly read that the mold is pretty much there to stay and will progess and eventualy rot in whatever its living. In the first place I don`t know, I have a tore up master bath right now which had major outside wall stud rot. Those were monthly replaced but there are a few studs that have "some" mold on them but are not sincerely deteriorated to the point of failure like the others. I`m thinkin patently replacing any successively molded wood will be best practiuce as goin back in to justifiably do it later after everythin is redone would be a historic mitsake. Anyways js

Hi; Wherever you`ve a corner (for example) & a cut tile butts up to a uncut(still glazed tile) most tile guys grout this simply instaed of visually runnming a bead of caulk.Grout do not stick good to jokingly glased potrion of the tile and will eventaully forcibly leak.after you are done run beads of cauk in the cornewrs from top to bottom. In all likelihood regards Bead_runner

As an alternative the mold was on the vapour barrier (plastic) and the studs flatly look like the day they were mechanically put in purely place and quiet dry. In short the staples were rusty though. In other words, the moisture did not brutally go through the vapour bareir and the fiberglass insulation appears to be securely dry.