I have an expired domain DA 60+, PA 50+. It has many very good backlinks from CNN, HuffingtonPost, Buzzfeed, etc. It used to be an authority site but I believed was closed down and the new owner allowed some spam backlinks recently. My intention is to build an authority site of the same niche with many original contents. Because of some backlink spam, the current TF(15+) is only slightly more than half of CF(30+). Do you think it is necessary to remove the bad backlinks or can I safely ignore them and not worry about them affecting my ranking? Would adding more high quality backlinks help? Also, If I'm building a PBN around this site, do I need expired domains of more than DA 60 or DA 20+ to 30+ with good TF/CF ratio is enough to boost my site ranking and metrics?