The p0128 if just for the coolant temp not getting up to proper temp. Replacing the thermostat and bleeding the system of air normally fixes it.

Having a misfire isnt good, I can't tell you if it's a hard miss or just at random. You'd notice a hard misfire quickly and it wouldn't be a good idea to drive it like that.It's not burning fuel on that cylinder and could end up overheating the cat converter and melting it down internally.

With your tune up, new plugs and wires should fix it, if not you just have the coil packs and ignition control module to look at for faults.