Possibilities: Fuel mixture is WAY too rich OR the timing is out of spec.
The answer is yes. A crack in a manifold is much worse than just the oil leak. Manifold cracks are generally caused by severe overheating or improper assembly of parts. A crack in a manifold can cause oil to leak but the oil leak is inconsequential as the crack renders the engine unusable safely, without replacing the manifold. Running an engine with a cracked manifold is very bad for the rest of the engine and your own safety.
Yes, it could. What could happen is it leaks as you are going down the road and leaks onto the exhaust manifold and creates the smoke.
It could.
Yes
it could be the center support bearing in your driveshaft
Absolutely, the manifold must seal to contain the compression the engine generates when the spark ignites the gasoline.
An engine might sound like a diesel at operating temperature if the engine was a diesel or if there was an issue with the manifold. Sometimes gases escaping the manifold cover could cause the engine to sound different.
it could be a head leaking or the intake manifold, if its coming from the very top its most likely the intake manifold gasket
Intake manifold gasket
o2 censor
Intake manifold leaks will cause the engine to idle rough and get poor fuel economy. An exhaust manifold will have no symptoms other than the sound of the leak.
No but an engine running like that can damage the valves.