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I think that depends alot on your isp I do know that some isps give whole ipv6 blocks.

And then you have to look if you need a extra isp connection, often with fiber some isps use a media connector then its easier, I believe you have to make a static wan with the data the isp gives you.

When I still hosted a server at ovh I could get a ip block via ripe by ovh, and then I had to create my own interface with ip, gateway etcetera, I think this is also how it would work on openwrt aslong your isp makes that possible.

But you can also ask yourself if you really need multiple public ips:

Sometimes you may have 2 appliances using the same port which gives problems, well you can use nginx for that if you own a domain name, you can make it that nginx proxy looks at the domain name and then uses the correct appliance ip and with SRP records on the domain provider you could also remove ports.

In case your isp uses a dynamic public ip, you could use ddns for this.

It really depends on your use case😉