The temperature inside will vary greatly from home to home, so you will need to adjust baby's clothing based on your house. The extra layer applies here too, so if you're okay with one layer, baby should have two. If you have two, baby should have three and so on. Check baby's temperature by putting your hand on her tummy or back. She should be warm, but not sweaty. At bedtime this is particularly important as overheating can contribute to SIDS. Choose a sleep bag based on your usual home temperature and then adjust baby's clothing accordingly to room temperature. A short sleeve onesie might be enough in warmer rooms, where as a warm, footed sleeper might be best in colder rooms.
In the car seat
If your baby is young enough to still go in the infant car seat, the less bulk the better. Stay away from car seat bags that lay inside the car seat, and instead opt for car seat covers that just covers the top of the seat. Swap heavy, puffy snowsuits for lighter ones, and instead, cover baby with blankets to keep warm. The reason for this is that all that bulk can compress in a car crash, creating a gap between the seat belt and baby and possibly causing injury. So as long as baby is being transported from one warm location (i.e. home) to another (i.e. grocery store) while being in a warm car, a fleece footed sleeper and a hat is good. For extra warmth lay a blanket over top of baby, or put his jacket on "backwards" so it's sitting on top and not laying behind baby.
On a walk
Layer! Babies lose heat faster than us adults, so always add one extra layer for baby when spending some time outside in colder temperatures. Start with a onesie and add a sweater or fleece/velour sleeper over top. Then a warm coat and bunting bag or snowsuit. Add a warm, snug-fitting hat that covers her ears and if her hands aren't covered in her bunting bag or snowsuit, make sure to add some mitts. Thumb-less mitts are usually best for babies. If her feet aren't covered, make sure you add some warm boots as well. Softsoled ones are usually best for baby as they stay on good while keeping baby's feet warm.
Once your baby is old enough to want to play outside, your emphasis should be on staying warm, but also dry. A heavier snowsuit, preferably with a hood to go over his warm hat, is a must, and look for waterproof boots and mitts. Under the snowsuit make sure you layer so you can easily adjust if he gets too hot while playing. Also, don't forget sunscreen and sunglasses as the sun reflects on the snow.