Build or buy a few GPSDOs, put a couple of antennas outside (up and in the clear), distribute the 1PPS to a few of your servers, put NICs that support hardware

Build or buy a few GPSDOs, put a couple of antennas outside (up and in the clear), distribute the 1PPS to a few of your servers, put NICs that support hardware timestamping in them, and make them your time servers (they'll run your NTP and PTP daemons). A dedicated VLAN for PTP will be helpful, by the way. Anything "critical" can run the PTP client in order to get time sync via PTP (on that dedicated VLAN). Everything else can run an NTP client. (That Raspberry Pi with a cheap GPS module probably isn't nearly as accurate as you think. In particular, its PPS is likely full of jitter. If it's "good enough" for you, well, that's all that matters.)