I like your approach here. I am doing something similar (also with iBGP!) but didn't involve FIBs or pf; I wanted automatic failover at my firewall across multiple internet connections at home (fiber and backup 5G/LTE). Also my setup has the cloud VPS' static IP on my home VNET jail on a loopback -- I use arp proxy to make it routed over a Wireguard tunnel.
I may have to borrow some inspiration from yours to make it even better. I really don't like the mss clamping down to 1220 though, it's so wasteful... *sigh*
btw, you have "hobgp" in the article where it should be "gobgp"
