My only rub with that is - shouldn't the router be only a router from a security perspective? Definitely combining servers for home use does make sense though.
Ideally yes. But with the resources needed for 25 Gbps, not using one machine for multiple purposes seems wasteful. The server only stores publically available data, though, so not a big deal from a security perspective.
Yeah running your nas-bittorrent/firewall-router on the same OS is clearly not something I would do, especially that now you can use somrthing like proxmox for example and virtualize your pfsense/opnsense instance.