Much depends on the code in your area. Here (MA), that wouldn't pass inspection because the shower and toilet aren't vented properly. The shower vent has to come off the waste arm for the shower, rather than the 3" branch drain. Also, you can only tie the vent for this new bathroom into the 3" stack if the other bathroom in the house is not dumping down from above. If it is, then the new vent needs to tie in 6" above the flood level rim of the highest fixture served in that other bathroom, OR run out through the roof independently.