The price of premises is HK$700,000
assume you use 95% mortgage for 30yrs
your mortgage loan = HK$700,000 x 95% + HK$700,000 x 3.98% (for mortgage insurance premium) = HK$692,860
now, the annual mortgage rate is around 4.5%. For 30yrs, your monthly payment is HK$3,510.62, which is less than half of your income (i.e. < HK$4,500). Creditability feasibility.
However, you have to pay 5% downpayment, stamp duty, 1% commission, solicitor fee, etc. The lump sum fee you have to pay is around HK$46,200
now, the monthly fixed deposit interest is 2.1%.
assume to deposit HK$1,000 every month for fixed deposit, then you can accumulate HK$50,000 after 4 yrs.
So, your planning should be keep saving HK$1,000 per month in bank for fixed deposit for 4 yrs, then buy your premises with 95% mortgage. But don't forget, you may be required to pay 10% downpayment, before your can get back the 5% excess from the bank after you get the 95% mortgage. You may have to find some bridging loan to financial that 5% for your during that period (around 1 - 1.5 months normally)