Overweight has nothing to do with baby bump. Baby bump varies from person to person. However for most, it starts showing by 18-20 weeks.

yes from mid of 4th month its very prominent. though depends on person to person

I started to show start of 5th month.

usually 4th to 5th months..

Baby bump started to show from 4th month.( An experienced elder generation aged ladies will know even before the bump. )