Using water from the display will not hurt but it will not affect the cycle to any extent (bacteria are not free floating) The power sponge filter in your sump/refuge for a few weeks prior will help a lot.
Failure to have a properly cycled qt tank is probaby the biggest point of failure I bet.
Even in an emergency, you can fire up the qt tank, monitor the ammonia and as soon as it gets out of hand, run water changes from your display to your qt tank, add the makeup water to the display tank. Sort of a pain but it works