Nop 3.x coding advise and help

Hello,
I'm an old Nop 1.0 hacker and I'm trying to mend my ways in transforming an old site to 3.9 using only the approved methods.
  
I've read many of these forum posts and gone through tutorials such as the Trial Tracker Youtube tutorial, but I'm still not getting the full picture of how to completely override Controllers, Models, and Views.  Views seems pretty straight forward, but the other two I'm not connecting all the dots.

Say I want to override an ActionResult function like "AddProductToCart_Details" in the controller file "ShoppingCartController.cs".  Assuming the best way to accomplish this is to create a custom plugin, my questions are:

1. Is it best to override the entire file, while changing only the "AddProductToCart_Details" function?
2. What are all the supporting files that need to exist within the plugin (not including references)?  
3. Assuming I would need a RouteProvider, what is the syntax for overriding this function?
4. Do I also need a specific reference to anything in a DependencyRegistrar.cs file?
5. Do we override Models in the same fashion?  Such as if I want to add an additional attribute to the ShoppingCartModel.  Copy paste the existing Model while adding the attribute or creating a ShoppingCartModelOverride.cs file that only references the new attribute?
6. Reference to the overridden model in the RouteProvide.cs or DependencyRegistrar.cs file?

If anyone has a comprehensive code example they would be willing to share, that could speak to all of these questions. I'd be willing to pay for your examples and/or (Skype?) time.  I just want to be sure to make my changes correctly.

Thanks!
[email protected]

Hi,

I Can assist you on it.

Please touch base with me over email: [email protected] OR Add me over Skype: cis.victor1

Thanks,
Victor

Hello Dhollis,

Check PM(Personal Message) for same.

Thanks,
Jatin