Also i belive Svätoslava's eyes are most "original slavic". I always imagine ancient slavs as auburn haired with eyes like Svätoslava. What do you guys think which eye colour was predominant among ancient slavs?

Definitely light eyes were predominant among ancient Slavs, but also I highly doubt one type was predominant among Slavs or any ancient European ethnic group of old. I would imagine blue or green eyes to be most common among ureheimat Slavs (which they still are today), though not predominant, since brown eyes are also common.