I use an N5105 generic mini pc running proxmox and opnsense. You can get them fairly cheaply from Aliexpress. They’re particularly low power and come with 4-6 gigabit network ports. I have two containers, the second of which hosts my Home Assistant instance. As an added bonus they often don’t have a fan.
For wifi I use Ubiquity wifi 6 Lite APs with the controller running under home assistant.
Hasn’t been an issue for me. HA would only be depending on Opnsense for a DHCP lease so assuming you have reasonable lease times it’ll just pick up where it left off.
Without checking I would imagine you could just set a delay for the HA container to make sure opnsense can start first, if it does become an issue.