u/browsing_soup as discussed earlier on your 2 router setup this is how one part of the problem(ARP …other is IP) start to arise.

Without looking at any equipment/kits first I’d suggest your viewership of videos from Cross Talk Solutions. I’ve included a few…

• Wireless design for a log cabin - https://www.youtube.com/watch?v=DkMQ3ynHcW8
• Grecian port wireless design - https://www.youtube.com/watch?v=zr6ehNyqddI
• Lakehouse installation - https://www.youtube.com/watch?v=P-bDxMgvG1I
• 6 mile rural point to point link - https://www.youtube.com/watch?v=esw8435oPN0
• 35 km point to point link - https://www.youtube.com/watch?v=SEQgvMdkTf4

Some aspects that would come to mind:

• Yes it’s a farm which I’d expect to be mostly flat but what’s the gradient/slope?
• With respect to the above any obstacles around the buildings or along the line of sight?
• If they are you may have to seek the tallest building/tower in your area that beams/bounces the network around… so does costs of equipment required for such distances & fees for placing your equipment on their property…

Tailscale.

Don’t punch any holes in your NAT aka port forwarding.

Regarding sharing media with friends and family how far away are they? How much of you upload will be taken? How will you deal with your apartments changing public IP(behind a CGNAT?) and theirs be it on mobile/cellular or even home wifi as described above(CGNAT)?

You might find the only feasible & quality-wise enjoyable solution to be if you and they had storage(NASes). Updates/uploads could “flow” from your end in non-peak(the night) to theirs …

I want to keep proxmox on it and build a vm with all the nic

What your creating is called the forbidden router.