The elastomeric paint is great for stucco, but isn't a good choice for the mural. Typically, elastomeric is available in a limited amount of colors and purchasing amounts smaller than 5 gallons could be difficult.
I have never used C2 Paints, it sound interesting. Any high quality exterior acrylic paint will work well for the mural. Use either a satin or semi-gloss sheen.
What effects the longevity the most is the stucco and how it is sealed. The stucco is your canvas and must be sealed before any paint can be applied. The reason for this is the stucco is very porous and will allow water behind the mural, causing peeling.
The elastomeric paint would make a great stucco sealer. If a colored painted back ground isn't to your liking, use an acrylic masonry sealer, I like Seal Crete. It is clear and easy to apply. Seal the entire wall or from expansion joint to expansion joint from top to bottom. This will keep the water out.
One more thing, allow the stucco to cure for 30 days before sealing and painting. Any sooner will cause peeling and problems.