Does my new soil pipe need additional venting?
The plumbing code and good common sense requires that you vent every fixture somehow.

I am not a plumber but in my reading of their code this branch would require a minimum of a 2" vent for the bathroom group run up to the attic and through the roof or terminate in an air admittance valve a minimum of 6" above the flood rim of the highest fixture (sink). (Some people hate AAVs, some say they are fine.) The waste line would have to be a minimum of 3" to the toilet and the shower and sink should have their own vents joining the main vent. These need to go vertical until they are at least 6" above the flood rim of the sink.

I am sure there are some finer points a real plumber could show you but the gist of it is: every fixture needs to be vented or you will siphon the trap and have sewer gas backing up into the house and boy will you be sorry then. A little plastic pipe now will save you from being very unpopular later.

Good luck!