That is a school of thought but after your 2nd you will have to fork out 30% though you could get 5% if you take a Sunway Loan Program which I did consider taking but decided against it as no way rental will cover a 95% loan.

My strategy tends to be 50-70% MOF, 25 years repayment, lowest possible interest rates on a full flexi. Rent for 5 years then sell or remortgage then hold for another 5 years, then dispose and buy the next one. If can't rent out at expected market price there will always be the option to lower the rental as a last resort.