Default Parameter must be Compile Time Constant. i.e

public void method(DateTime StartDate,DateTime endate=default (DateTime))
 {
 /*Accepted **/
 }
 public void method(DateTime StartDate, DateTime endate =DateTime.Now)
 {
 /*Error:DateTime.Now is not a Constant.you can only bind only compile time constants
 * **/
 }

Ref and Out are same for CLR and they both have same instructions.Only Compiler differences it for Developers Perspective. Instructions From IL Code below for ref and out methods. And this is the reason why we cannot have overload method with only difference as out and ref.

You cannot overload method with only difference of ref and out parameter.

private static void method(ref int refvariable)
 {

 }
 private static void method(out int refvariable)
 {
}

Its not possible.Compiler Error:Method with Same Signature Already Exist.

public void Method(out int i) { } //Error
public void Method(ref int i) { }//Error

We Cannot Overload Method with only difference as out and ref. It will 
throw Compiler Error.(Member with Same Signature Exist).

int NormalVaribale = 1;
 int referencevariable = 1;
 int outvaraibale = 1;

Normalmethod(NormalVaribale);
 referencemethod(ref referencevariable);
 outmethod(out outvaraibale);
 Console.WriteLine("Normal Variable"+NormalVaribale);
 Console.WriteLine("(REF)Reference Variable"+referencevariable);
 Console.WriteLine("(out) Out Varaible"+outvaraibale);

ref :Value must be Initialized before it is passed to the method. Reference is being passed to the method,so the value changed will get reflected./*It has got Nothing to do with value type and reference type both of these can use ref*/

out:Value need not be Assigned,but has to be defined before the method exists.

Note:Even though you have initialized before passing to method,you got to assign value before the method exists.

1.Static Constructors cannot have Access Modifiers  or have parameters.

2.They are initialized before  any static members are referenced.They are the First One to get Initialized.

3.A non static class can have static constructor.

class Test
{ 
static Test() //cannont have access modifier
{
Console.WriteLine("Hello World");
}
}