Maybe its just me but seems a little overkill. You should be able to run a 2" pipe from the stack and elbow it towards the 3" drain, then use 'Y' connectors to attach drainage for the shower and sink. (instead of running 3 vent stacks)
Also, you may want to check to see how far away the toilet drain is from a 3" stack. If its a bungalow you probably are pretty close to one.