Are congenital defects the same as birth defects?

Yes. Here is a primer on the terms congenital refers to being present at birth. Anomalies, abnormalities, defects are often used interchangeably. Not all are genetic or familial. Malformation and deformation mean different things. Malformation is an anomaly due to abnormal formation of a structure. Deformation is a change in a structure due to forces like pressure, eg, in cases of low amniotic fluid.
Yes. Congenital means "present at birth". It is the more scientific term for a birth defect.
Yes. They are referring to the same thing; birth defect is more a colloquialism/vernacular, congenital is usually used in a medical/scientific context.
Yes. Yes they refer to the same thing. They are abnormalities that develop while the baby is inside the uterus. They can be caused by genetics, toxins and drugs, or unknown reasons.
Yes. Congenital literally means "with birth". Birth defects can be from organs being formed wrong early in pregnancy, infection and exposure to harmful substances. The best thing you can do to avoid birth defects is to talk to your doctor about getting pregnant before you do so that any risk factors you have can be avoided.