Well depends on where you are. There are some very good lawyers who practice in 1 form of the law and become very good at what they do. Like if you wanted an Accident and Injury lawyer from where I live I can give you the name of a great lawyer who wins the largest amounts. Lawyers are more specific to area and there are some crappy lawyers out there.
This is general information, and varies greatly by state and even city. Also, many of these can be charged as either a misdemeanor or felony, and depends on the officer and details of the incident.
Driving under the influence? - Usually a misdemeanor unless there is an accident.
Driving under the influence while too young to legally consume alcohol? - Usually not different than if they were of age.
Reckless driving? - Again, depends on if there was an accident, and if the accident resulted in death/serious injury.
Assaulting a police officer? ( Pushing or shoving which also includes resisting arrest ) - Yes, battery against a peace officer is a felony, but just moving around or trying to run is resisting arrest which is a misdemeanor.
Selling parts off of a vehicle that wasn't stolen by you? - Felony
Committing a crime that is not a felony but fleeing into another state? - Felony, but only if a warrant has already been issued on the misdemeanor.
Committing a crime that is not a felony but fleeing into another country? - Again, Felony if a warrant was issued prior to leaving.
Stealing something that costs under $100, $1,000? $10,000? - Each state has a set amount of money when it changes from a misdemeanor to a felony. My state is set at $250, so a theft of $250 is a felony, and a theft of $249.99 is a misdemeanor.
Assaulting a police officer? ( Punching or kicking which also includes resisting arrest ) - See above
Assaulting a police officer? ( Verbally ) - Not a crime to say anything to a police officer
Assaulting a police officer? ( Grabbing for gun ) - Felony
Refusing to leave vehicle? - I am assuming you are saying that you are refusing to leave when an officer tells you to. That is going to be obstructing a police investigation and/or resisting arrest which are both usually misdemeanors.
Refusing to give up a gun in your possession? - Refusing to give it up is an obstruction misdemeanor, but if they want you to give up a weapon, it is usually for a felony possession or assault charge. Refusing if it involves threatening body language can land you a assault with a deadly weapon charge which is a felony.
Hitting a cop with a car? (No injuries, Injuries) - If it was done intentionally, it will get you a battery against a peace officer charge which is a felony or even an attempted murder charge. If it was an honest accident that just happened to involve an officer, it would be the same as any other accident.
Not all at once. All individual crimes by different individuals. Obviously all of these together = felony - FYI - Not actually true. If you have 10 misdemeanors, it doesn't "become" a felony. You have to commit a felony level crime to be charged with one.