1. Refinancing of the house for cash out portion

I would recommend refinancing the FULLY paid off property because you are not bound to the rule where the refinancing portion is limited to just 10 years of repayment or DSR calculation. If you refinance a house that already has a bank loan on it:

a. The refinancing of the outstanding portion's installment will be calculated  at a maximum of 35 years.
b. However, the cash out portion's commitment when calculating your Debt-service ratio (DSR) will be calculated at a maximum of 10 years. This will effect the maximum amount of loan that you would be getting.

Keep note however that banks like OCBC, Alliance, and HongLeong allow the repayment tenure for the cash-out portion to the maximum of 35 years, but you need to pass the DSR test as mentioned above first.

This is why I recommend refinancing the fully paid off house. As such, when you refinance that house, do it at full 90% and use the cash to to pay off the higher deposit, and lower loan amount for the new properties you want to acquire. With this method, you simply borrowing using one property to buy another. It's beneficial since you get to have cash in hand which you are free to use however you see fit.

2. Loan tenure

Now, I would still recommend applying for the highest loan tenure due to the flexibility of banks nowadays with advance payments that will offset the loan outstanding amount. As such, if you sign for 35 years tenure and repay your loan as if you had signed for 25 years tenure, then you will end up paying the same amount as someone who had signed for 25 years tenure anyway - your advantage would be that you have the flexibility of reverting to a lower installment if you need to (during financial emergencies)

3. Loan eligibility

Here is my calculation of your loan eligibility based on 85% DSR. Keep note that banks have different DSRs, some lower, other higher than 85%.