Is it sufficient to sterilize my bottle once a day in the morning using boiling water (soaked for 5 mins)? After that, after each use, wash them clean and use hot water to rinse the bottles (instead of soaking) ?

Typically, hot water, soap and some scrubbing is sufficient to help clean the bottles. From what I've heard, it is recommended that the most important time to sterilizer a bottle is when it is newly bought, before the first use. Soaking once a day should be fine as long as you wash the bottles (with hot water and soap) thoroughly after each use. :)