Can the vent just go outside and have a downturn on the PVC? It is not required to run up the entire outside of the house? Also how long can this vent pipe run? Must it be a strait line or may I have a 90 degree turn so I may run it where I want? Also can I run the sink in with the shower drain since they are both on the same wall> Using a Y to add the sink in?

Sanibest toilet installation allows for the pump vent to connect into the plumbing vent system... review the installation manual online if needed.. shows exactly how to vent these ( Installation of pumps, grinders, and toilets for the home | SFA ).

Yes, you can connect the sink into the shower drain and in most states use the sink drain and sink vent to WET VENT the shower... just need to increase the sink drain and sink vent to 2".

Mark