Linode API trouble provisioning linodes manually

I'm following this guide on installing FreeBSD 12.0 on Linode. The process involves provisioning an empty instance, adding disks+configs and then booting into rescue to download the installer (and so on).

I was able to get it working (with 13.2-RELEASE) by running commands using the CLI but have been running into issues waiting for the instance to be ready after provisioning.

At first I polled for the "offline" instance status and that seemed to work okay.

Now I'm trying to retry any calls that fail with a certain error code but I'm getting an endless stream of Linode Busy. It's definitely past how long I waited while doing this by hand.

What would you like to name your host?
testy
Creating g6-nanode-1 named testy.lb-zone.xyz
Waiting for testy to provision
provisioning...
Done provisioning
400: Linode busy.; 
('400: Linode busy.; ',)
400: Linode busy.; 
('400: Linode busy.; ',)
400: Linode busy.; 
('400: Linode busy.; ',)
400: Linode busy.; 
('400: Linode busy.; ',)
400: Linode busy.; 
('400: Linode busy.; ',)

I'm aware that this is "unsupported" but I feel like someone has figured out how to wait for a Linode to be ready for further configuration after the instance is created.

Here's the relevant section of the source if anyone's interested -- I'm no Python expert so it's a little crude. I also don't love the polling but can't see many other options. Open to suggestions.

while True:
    try:
        self.instance.disk_create(root_mb, "root", "raw")
        self.instance.disk_create(installer_mb, "installer", "raw")
        self.instance.config_create(**self._boot_config)
        self.instance.config_create(**self._installer_config)
        break
    except ApiError as apiErr:
        print(str(apiErr))
        print(apiErr.args)

        if is_linode_busy_err(apiErr):
            sleep(8)
            continue
         else:
            raise apiErr

Side note -- is there a better way to match a specific error? The semicolon and the space at the end of that string arg seem very weird but I haven't peeked at the source.