I am not a Rodnover, but I can answer you about creation. Due to Slavic mythology, there was a light, sea and Svetovid (in the guise of a swan). He felt alone, but he have seen his shadow on the water. He separated the shadow and the body connected with this shadow – they became Svarog and Veles.

Svarog and Veles were tired of monotony of sea and they created a land. Later there were some Veles' intrigues to rule the world alone, but he couldn't managed. Eventually, Svatovid decided to give to Svarog the earth – he had became a god of fire, sun and earth. Veles on the other hand became a god of underworld – with souls of the dead.

But originally, due to this myth, there was "something" before they created the world, so I assume there was a universe and gods didn't created it.

I can be wrong as I am not an expert in this mythology, but as far as I know, the creation of Earth was about like I said above.