Yes, so called "dry" sand is good enough. As bro terryansimon said, you can seed it by getting some sand from matured tanks.
As for the macroalgae, I am still distrustful of caulerpa as it tends to crash suddenly or go asex and pollute your system. Its toxins are also suspected to decrease coral growth too and they grow so fast, you need to prine them frequently. I would recommend chaeto or ulva instead but for cases like me who do not use macroalgae for nutrient export, try growing the slower growing ones.
You might also want to read my article on sandbeds first to get an overview on the dynamics