I am formulating a seed mix that can be planted along the Wasatch Front at elevations 4,000-7,500', no irrigation, broadcast seeded, with precipitation 20" or so annually (highly variable with drought conditions). This mix should be a (mostly) native mix of grasses and wildflower forbs. There are invasive species present that will take over the sites (construction or herbicide treated areas) unless restoration seed mix establishes quickly. The mix needs to be hardy - bordering on weedy or it will fail. We have used mixes with primarily wheatgrass in the past and it is too slow growing and has failed, the mix needs to be diversified. 

*crested wheatgrass is out and we will not use it in this mix

Questions:

Will I need a few introduced species because the natives cannot compete with the quick germinating invasives?  I am leaning towards yes. 

Is there a rule of thumb for total number of different species you should use when formulating a seed mix of this type? (i.e. how many different varieties of wheatgrass is too much?)

What cool season grass species will germinate quickly and help prevent the ruderal strategist species like cheatgrass? We usually do our restoration in fall or early spring. 

Smooth Brome is not on the attached list but I was considering it because it is so hardy. 

A  list of species I am considering is attached. Any advice would be appreciated! 

Thank You.