Did it start rough both before AND after the spark plug change?
What kind of spark plugs did you install?
Has the throttle body ever been cleaned out?

“...sometimes the starter is fighting against what seems like a strong kick back. The engine rotation almost stops briefly before rotating again...”

Is there smoke out the tail pipe when first started? If so, what color?
Is the coolant level dropping?

I’m wondering about a leaky injector. Here’s something to try - when you shut the engine off, immediately release the residual fuel pressure out of the fuel rail Schrader valve into a rag. Then see if you still experience the cranking “kick back” and rough idle the next time you start it up.

Is the problem worse after it sits all night or after a five minute visit to the store?