One of my colocated servers has 60TB of space to spare and has a 10gbe unmetered uplink on the provider's IP-transit blend.
It is easy to configure traffic shaping on the box so that any unused upload bandwidth can be used without any impact to existing applications.
I would be happy to seed NixOS torrents. There is an extension to torrents where files can be added to a torrent after a torrent is released that might make sense to look at.