1. If you use a screen the shower will be "clogged" continually.Originally Posted by Agewon
2. Al the fixtures need to be "revented".
3. The toilet and the basin require vents regardless of the size of the drain pipe.
4. The arrangement of the fixtures is immaterial as long as they are properly piped and vented.
5. It can be "bad" under certain specific situations. But since you must have at least one "real" vent, and the distance from the lavatory to that vent cannot be very great, why take the chance?
6. Whatever it takes to install them. It depends on how deep your pipe is to start with.
7. Unless your main drain is leaves the building above the floor, why are you using a pump with all the extra cost, maintneance, and potential failures a pump is prone to?