Ajenti V is a plugin to Ajenti. Ok so did you press the "Enable" button that says "If you press this, configs for NGINX, PHP-FPM, etc etc will be destroyed"?

Did you install Ajenti or Ajenti V as well too?

Yes, you can have multiple values with colon. If you remove the value, it defaults to <website path>:/tmp

Looks like you just stopped some backend service of your website on the way. NGINX section of Ajenti doesn't work for you because you don't have standard Debian "sites-available/sites-enabled" config layout in /etc/nginx. This however can't cause your website to stop.

Please post content of /etc/ajenti/vh.json (or send it to e@ajenti.org)

Username: test@example.com
Password: your password
SMTP server: server's address
IMAP server: server's address
Ports: default ones (SMTP TLS and IMAPS if you have configured TLS for Ajenti V mail).

If you have /owncloud Content entry and /srv/owncloud website path, check that "Append path to URL" checkbox is unchecked in that Content entry.

Probably your content path isn't pointing to an existing directory. You can read errors in /var/log/nginx/<website>.error.log

The config looks cut. If self-tests are ok, and maintenance mode is unchecked, you shouldn't receive 503 anymore.