Thx. Better to compare the 2070 Super to the 2080. Its around the same. More hash more price. But the ratio is nearly the same.
If you go for used, you will find more 2080s and might geat a good deal. I never payed more than 550 EUR for a 2080.
If you want to go for more GPUs, the 2060 super isnt bad. 8GB Ram. I prefer less rigs and more hash.