New here with a few questions

Current bike is under construction and it will run a CT on the rear as soon as I can figure out which tire. It is a Paughco rigid Swedish style frame and the rear wheel I have for it has a junk 180/55r-18 Dunlop ripe for replacement. I'm not too worried about clearance, frame is set up to accept a wide tire and fender has not been picked out yet. as long as I clear the chain I'm happy.
So far I'm finding limited tire options for the 18" wheel, Any recommendations?

Second question, how important is tread design? I have noticed several tire manufactures do not have a symmetrical design to their tread, with the inboard & outboard looking different. I would assume that is not good for a bike, Right?

Well, popped a 205 on there. Looks like it will work.

Apparently this site is stagnant. I have found no problems with any tread pattern, symmetrical or not.