base coat clear coat wet sand, and now what?

I see no reason at all why you could not lightly sand with 600 and respray clear. You just need to sand enough to leave 600 grit sanding scratches for mechanical adhesion. Don't sand enough to go through the clear. light sanding with 600 should not take off too much material. Should be no problem. Using a 1.4 tip will be no problem. I have successfully sprayed clear with a 1.5 tip.