1. For employees with salary over 5k, they are protected to the extent of what are stated in their contract of service. These employees should see to it that when they sign the contract of service, the terms and conditions such as salary, medical benefits, bonus payment, working hours, leave entitlement etc etc are cleared stated. They can sue in the event of any breach. The civil laws, the Industrial Relations Act give them the protection.
2. You still have to look at what have been written in the contract of service. Anyway, unconfirmed employees are equally protected by the Industrial Relations Act as far as employment is concerned.
3. I am not aware of such a requirement. Airlines may have such stringent requirement for their air hostesses.
4. I am not sure if it is a good ground for terminating an employee's service. Better don't try it.
Please be aware that I am just sharing what I know and those are not expert opinions.