The tub will need a vent, and the shower will need a vent.
If the center of the drain is over the 4" line, you can offset your tub drain with fittings to the side.
Anything coming off the main line horizontals will need to be wyes.
Between the p-trap and the main line, you will need a vent. Otherwise, water running down the main line will siphon the p-trap.