A friend's cousin wants to install a washroom in his basement which is already finished with tile on the floor. We already know we have to break some of the tile/concrete floor as there was no rough in for the basement washroom. The owner wants a stand up shower BUT with a shower pan (not tiled). Walls and ceiling of shower will be tiled but he wants to use a shower pan. I've never installed a shower pan so I have couple of questions...

1. Should I remove all the tile where the shower pan is going to be installed. We are already going to have to break some of the floor to install the drain but is it necessary to remove all the tile for under the shower pan? Is it bad to leave the tile under?

2. Do you need to put anything under these shower pans (liner, etc.) before you install to protect the concrete/tiled floor?

3. Once the shower pan is installed and the 2x4 walls are built around the pan and drywall is up (durock). Can I apply RedGard at this point or do I have to tape the seams?

4. Do I leave a 1/8"-1/4" gap from the bottom tile to the floor pan like a bath tub? Is it better to silicone that gap or should there be grout or grout with silicone over it?

Any help would be much appreciated as I've never installed a shower pan before. The owner is dead set on using it too so lets forget about changing his mind.

Thanks