No. Thinset or tile glue (adhesive) should never be applied directly to the shower pan liner. 

The recommended thickness for this pour is between 2” to 3”. This is the minimal thickness starting at the drain, then sloping up and away from the drain at a ¼” per foot. This is not always possible due to curb heights. If this is true, pour as thick as possible and consider a higher quality cement which will allow for a thinner pour while maintaining strength. 

This depends on the quality of the cement products you are using and the minimal thickness recommended by that specific manufacture. The normal rule is ¼” thick starting at the outside of the flange, then the concrete is sloped up and away from the drain at ¼” per foot.

Oateyweld

Oatey X-15 Shower Pan Liner Adhesive

Oatey has approved the three following Liquid Nails products for this application. LN - 609 / Panel & Foam Adhesive  LN - 715 / Tub Surround & Shower Adhesive LN – 915 / Tub Surround & Shower Wall Adhesive

Mushroom Vent Caps can be attached to any vertical sanitary vent pipe, in order to keep debris from falling into the pipe. This doesn’t apply to septic tank vents which rise vertically out of the ground, and then turn down (looking like a candy cane).

No. This product is not intended for use in any plumbing system where plumbing codes are enforced. 

No. As the cable and cutter pass through the valve, the flapper would be damaged. Once the cable passes by the flapper, it would not be able to return because the flapper would close down on it. This would cause permanent damage to the flapper. Cleanout Tees should be installed on either side of the Backwater device.

You will have to pay attention to the drains for signs that the Backwater valve is closed. If the valve is closed the water will not be able to pass through it and will back up through the lowest drain in the home (floor drain or shower base in the lowest level of the home). The drains will also gurgle as water is being let out of the fixture.