Hello Benoit Nesme.

1) In many things documentation of 5.0 is similar to 4.6.

2) TransactionalAttribute and NotTransactionalAttribute are based on PostSharp. Due to PostSharp is no longer in use we removed them. In 5.0.x there is no something simmilar.

3) Enum fields has same names in 5.0 and 4.6. By default enum field Company.CompanyType will generate column with 'CompanyType' name of 'Company' table. Are there any [FieldMapping] attributes on those enum fields? If so, then you can keep mapping. DO might resolve it if names of fields are same. 4) You don't have to do it manually. DO checks registered assemblies. If any version of assemblies then DO try to find upgrader. Write something like

public class SecurityAssemblyUpgradeHandler : UpgradeHandler
  {
    public override Assembly Assembly
    {
      get { return typeof (GenericPrincipal).Assembly; }
    }

public override string AssemblyName
{
  get { return Assembly.GetName().Name; }
}

public override bool CanUpgradeFrom(string oldVersion)
{
  // you can filter specific versions of assembly here.
  // this implementation will be used for upgrade from any versions
  return true;
}

}

...
domainConfiguration.Types.Register(typeof (SecurityAssemblyUpgradeHandler));
...

Validation framework was reworked very much so, unfortunately, there is no access to ValidationContext (it is another ValidationContext now), also there is no any replacements for Session.DisableValidation(). If field has Constraint it will be validated on transaction committing or on changing of field value.

What for do you use ValidationContext and Session.DisableValidation() in 4.6? Maybe I can find some workaround for you.