Slow starting, then starts up. battery checked out fine.

Check your battery cables. The battery cables could be routed by engine or exhaust components that get the cables hot which in turn will cause resistance and cause the slow cranking. The fact that it starts fine after sitting tells me something is probably getting heat soaked. If you're sure it's not the starter I would check the cables and especially ground connections to the frame, engine block, and body. Check resistance with a multimeter if you are able. If they are the original cables I bet that's it. If the starter and alternator are good then the cables are probably at fault. I would also check the starter relay but that wouldn't cause slow cranking..

You need to address those misfire codes, have it tested again.

happens a lot to boats due to close prox to water , corrosion on both ends of battery cables , this corrosion looks like powdered white material and can occur even inside battery switches

You may potentially have an serious electrical drain in your car circuits. The drain is slow and continuous, draining your battery charge even if you do a start. Check the cabling and look for load on your battery with a Volt meter to check for any charge drainage. Check this as a precaution before replacing any more parts.

Not the coil, wouldn't affect or be affected by the slow starter. I would double check grounds and battery, starter, and alternator connections for a clean tight connection. I would be looking at doing voltage drop tests to look for high resistance in the start circuit.
You may have to get under the dash and find the source of the smoke. Sometimes the back of the fuse panel where the wiring connects in will get so hot the plastic starts to melt. Then the wires and connections go bad, and you can even have current cross feeding into another circuit-like your wipers are doing. So I would pull off the fuse box and check for that. Keep looking for something that burned. It's got to be electrical.
Starter and solenoid being only 2 years old, should be good. But if starter to battery positive post has no high resistance in that connection, and battery ground is known good, and if the small (?purple?) wire to starter solenoid has battery voltage or very close to it, when checked with a voltmeter while the key was held in crank, then you might want to have the starter taken off and tested. The solenoid will be tested as well. If when you checked the small wire to solenoid with key in crank, and had much less than battery voltage, like 5 or 6 volts, then problem is in start circuit between the ignition switch and the starter solenoid.
Good luck. Let us know what you find out.

It could be the cold weather. Cold cranking amps could be down.

What year of Kia? 2013 Kia/Hyundais have defective starters.Is it the cranking speed that is slow then faster?

When you say slow start do you mean it cranks slow of cranks along time before firing?

Check standing battery voltage after sitting overnight. Battery may not be in very good shape, after starting, it will develop a surface charge that helps during subsequent starts. A starter that is drawing too much amperage can also cause this. Also make sure glow plugs are good.

Sounds like you may want a starter draw test performed, also you may have a basic draw test done, that will tell you if your car has excessive draw on the battery that is causing the slow cranking.