Ok, so I used your commandlines, substituting domain-controller for wordpress. Create reported no errors but start isn't happy.

root@lxc ~# cat inithooks.conf
export ROOT_PASS=secretrootpass
export DB_PASS=secretmysqlpass
export APP_PASS=secretadminwppass
export APP_EMAIL=admin@example.com
export APP_DOMAIN=www.example.com
export HUB_APIKEY=SKIP
export SEC_ALERTS=SKIP
export SEC_UPDATES=FORCE

root@lxc ~# lxc-create -n domain-controller -f /etc/lxc/bridged.conf -t turnkey -- domain-controller
INFO [lxc-turnkey]: begin creating container domain-controller...
INFO [lxc-turnkey]: downloading appliance signature debian-9-turnkey-domain-controller_15.0-1_amd64.tar.gz.hash...
INFO [lxc-turnkey]: no change in appliance signature...using cached image...
...snip...

Ahh, so create also dowloads, and, downloads are cached, great!

But: 

root@lxc ~# lxc-start -n domain-controller
Container domain-controller not connected:
root@lxc ~#

Tried starting again:

root@lxc ~# lxc-start -n domain-controller
lxc-start: tools/lxc_start.c: main: 301 Container is already running.
Container domain-controller not connected:
root@lxc ~#

Ok, so something is doing something. `ps ax| grep lxc` shows a single process:

20432 ?        Ss     0:00 [lxc monitor] /var/lib/lxc domain-controller

The DC doc explains there are some additional steps, but at this point I don't know how to get to the DC lxc machine in order to do them. Where does the container go? With the template command target folder was a required parameter.

Well, off to do more exploration and testing.