Hello SG 2011,
Third party reference would be your vendors and regular customers. You may attach 1 or 2 letters from your vendors and 1 or 2 from customers and 1 from your employee.
Vendors: This could be any vendor or supplier you have been dealing with for a while now.
Customer: This could be your long term regular customers.
Then include one from one of your employee as well. Any senior long term member from your team at the restaurant.
Regarding Docs:
Please submit your Trade License, Registration documents and any other document you think you will need to provide to prove the existence of your business.
Basically please view it in this perspective. You need to prove 2 things:
1) Proof of your duties and responsibilties (the third party ref letters are for this purpose).
2) Proof that your business exists, and that you are the owner of this business, and that your business runs as a restaurant. (this the docs mentioned will prove).
You just need to take care of these 2 things, and you're home safe.
Should you require any further clarifications, please feel free to ask.
Good luck with your application.
By the way, just a piece of friendly advice. Please gather everything really fast and apply as quickly as you can, as the 0631 category is filling up VERY FAST.
Cheers