The WRB is not only a code requirement but it is something you just don’t want to screw around with. Try to purchase the best system you can afford, ideally a ‘smart barrier’ that is resistant to bulk water but at the same time open to vapor diffusion so that the wall can dry to the exterior. 

There are many options for the structure of the wall. We’ve pretty much tried them all, including 2x4, 2x6, double 2x4 on a shared/split plate, SIPs, ICF above grade, Superior Wall above grade, vertical I-Joists, etc. We’ve studied the costs of different wall assemblies and it amazes me how similar these are if you evaluate a wall based on thermal performance alone.   

Every few months (weeks or even days) in our office we discuss the pros and cons of different wall assemblies in the context of a wide variety of projects. Every project has different goals and every client or builder has a different set of values when it comes to material considerations, thermal resistance, embodied energy, lifecycle, costs, etc. There are as many different opinions about the best wall assembly as there are people who design them. 

There is a myth that has been perpetuated in design schools, trade schools, home improvement magazines, TV shows, and online that building in even units of dimension is easier, more cost-effective and conserves material resources.  This is partly right but mostly wrong. 

Where to get info on the latest building science

An explanation of the many meanings of STREAM.