White smoke then water vapor

If you still have the old plugs look at them close. Does one seem to be much cleaner than the others or have a glazed look? If so the issue you have is a coolant leak into the combustion chamber, either a bad head gasket or a cracked engine component. The coolant would be the reason for the smoke and water vapor both. A leak down test or compression test would both tell you more but that is what you describe.
This might explain the testing better.
https://www.2carpros.com/articles/head-gasket-blown-test

Hello,

Yes, I'm sorry to say that it is telling you the head gasket has gone bad. The heater blowing cold air is showing that engine emissions is entering the cooling system and the white smoke is the coolant entering the combustion chamber and what your seeing is steam. Having both mean that most likely the head is warped as well and will need to be resurfaced. Most of the time It's all a top end job and unless a severe overheating took place the block is probably fine but its important to get that water oil mix out of the engine or the crank bearings may become compromised from the water in there. Your initial rough running was probably due to loss of compression from the head being warped. Was this car overheated lately?
Tom

P0301 is a misfire code for cylinder 1 which points to that being where the coolant is getting in. P0300 is a random misfire code which means that there are more than one cylinder misfiring but there are not enough misfires on the other cylinders to show what one other than cylinder one.
I suspect the issue is between cylinders one and two and is very likely the head gasket, but until the engine is apart you won't know for sure.