Simple Joys Kid's Pram Ivory Bear Outerwear

Can this be worn over a onesie in the car seat safely?

How many inches is the newborn size from shoulder to heel?

Is this warm enough for a stroller in below freezing weather without a bunting bag over it?

My baby is due in january and i want to get this to take her home in. should i buy newborn or 0-3 months?