It may impact your choices to know that plant material has very little effect on noise reduction and that a single plant width hedge or screen will have virtually no effect, regardless of plant choice. The only way to effectively block noise is a solid surface - a fence or wall - and one of sufficient height.

FWIW, Chinese privet is an invasive species in many parts of the country and I'd avoid planting this if it shows this predilection in your area. And Cryptomerias develop into pretty good sized trees and shearing or hedging them to maintain a height of 8' is not a good idea. There are dwarf or low growing forms but they tend to grow very slowly as well.

Have you checked with local garden centers about what they might recommend appropriate to your location?

Raise the height of the wall, if possible.

As has already been said, plants alone will not attenuate noise. Even an 8 foot tall solid wall will do no more than deflect some noise, but you will still hear it. In your situation, all you can do is visually screen the traffic, but if you want to drown out the noise, you'll need to add a counteracting white noise such as falling water or rustling of bamboo foliage, etc.

Personally, I find a hedge of one type that is well kept to be more tasteful than one that alternates species, unless they are done in a more organized fashion of block plantings that may overlap or be staggered. Symmetry tends to correlate better with uniform plantings, and a trimmed hedge softened by a contrasting lower or taller natural form is an easier way to get a natural look contrasted against an architectural backdrop hedge.

Don't count on plantings to do anything in the way of noise reduction, add your own more pleasant noise instead to drown it out.

If you were able to add a 3 to 4 foot tall berm between you and the street and had a solid 5 foot wall at the top of the berm, along with trees/shrubs/or bamboo that rustled in the wind, you'd also fare better at reducing the decibels inside your hedge/wall.

my house is up a slope from a busy street. what kind of wall should I construct to reduce traffice noise, and how tall?