First I would re-sheet the wall with villaboard, these arcrylic shower kits come with a glue that recomends villaboard, over time it will just peel off the plaster.
With the few that Ive installed I havent worried about waterproofing the walls but the unit must be well sealed, using kitchen and bathroom silicone, which brings me to the next point, the base.
The first one I installed was on a bed of sand and cement, it ended up moving then it would 'crunch' under your feet when you walked in. Since then Ive used liquid nails with no hassles. You then must seal the perimeter of the base with sikaflex, then waterproof your floor.
Then you will need to screed a sand and cement bed for the tiles, the compressed fobro floor sheets move around too much to simply glue tiles down, all the grout cracks and falls out then your tiles crack and/or become loose. And yes you will have to mix up your own mix. Give it a go, it will be an adventure!![]()