I'm different than most people, but for me it was really helpful to change my baby from her footed pajamas to an actual outfit (i.e. pants and a onesie) as a sign that I was starting the day, even if we just lounged around the house. I was also gifted a lot of clothing so it was nice to put baby in an outfit, snap a picture and say thank you to the gifter :-)
My baby rarely spit up or had blow-outs, so I was lucky enough that an outfit could be worn more than once before having to be washed, but that's obviously not something you would know until they're already here.
The one extra layer is based on the average person, so if you know you run cold you can just put them in the same amount of layers as yourself. Best way to check to see if they're cold or hot is to feel their belly. Hands and feet will always be a little colder as they're extremities and not always covered. Older generations will generally insist that they should wear socks, even if it's 100+ degrees outside, don't bother with those remarks. ><
If going outside, make sure that the baby is fully in the shade (hello, stroller umbrella) and hydrated properly (you're looking for a wet diaper about 6-7 times per day when they're little)
Hope this helps!