adding a node and instance to physical standby

I am planning to add an instance to a newly added node on a physical standby database, node has not been added on the primary side. What kind of problem can I run into if add instance to my new node on the standby first with the hope that I will do the same on the primary in 2 to 3 weeks. I am running 11.2.0.3 RAC database. I currently have 3 nodes on the primary and 4 nodes on the standby side with 3 instances on both side.