Advices for self-employed/business owners? Advisable to contribute to CPF?

Yes, you should contribute to CPF as it gives you an added protection in the event your business goes south. And paying yourself a salary is also advisable as this is one of the important factors banks look at if you need to get a loan.

Yes. I do self contribute to my CPF as it will help to deduct taxable income and at the same time this will also help to build my retirement fund or I can also use those funds for housing.