slicks work great on pavement even in sloppy weather.
Now if you hit some muddy/dusty/gravel sections, then treads might help.

Usually you want the good tire on the front because the constant steering adjustments are what keeps you upright. If you can't steer, you will go down. If you blow a rear, you can still control the bike to a stop.

You can just put the new tire on the front, and move the old front to the rear.
Front tire wear is about 33% of the rear.