If you muse over how the sparkplug works as a threaded device, it comes to
mind that the crushable gasket acts as a minor gas seal and also a minor
locking device.  For all intents and purposes there is no significant force
on the plug.  Similarly the plug is not designed as a joining device so the
holding torque need only be enough to keep the plug in the threaded hole.

Using anti-seize is a very good idea as the plug and the aluminum head have
different coefficients of expansion.  It also prevents to some degree
electrochemical reaction between the iron and the aluminum.  No need to
worry about the spark circuit, there is plenty of EHV conductivity in the
areas where you didn't apply the a-s.

So tight enough to not pass gas.  Sorry Terry.