Shower Waterproofing

My shower plan is to square / plumb my shower walls (3 sided). Add permabase cement board to the ceiling (8’). Add a Schluter/Kerdi curb. Mud deck the shower floor sloped to drain on one end with a Flow FX drain. Apply Schluter membrane to entire area using Laticrete Multimax.

Am I thinking right?

I want to add a custom niche to back wall but can not find any Schluter/Kerdi 1/2” foam board anywhere.

Option 1. Build niche out of Sentinel foam board from Floor and Decor. (No positive reviews or information on this product.

Option 2. HELP?????