I put collars on my pups at 3wks old.
This year I had 6 b/w with identical markings.. so this kept the right pups with the right litter [um, after I had switched two inadvertantly and my son noticed it! lol].
I also have the kids [all the kids friends that come over each day] holding pups constantly from birth.
My pups are bomb proof … there isn't a noise or person that bothers them... all noises and people are just "there" and no big deal.
Until 7-8 weeks you cannot make a final decision which pups go where, so calling them by other names is kind of hard. You can give basic names but be well aware they will be changed.
I say 7-8 weeks because you aren't going to have puppy eye exams until at least that age... final decisions should not be made prior to that appointment, IMO.
We don't generally have more than a week of teen temperatures.. so my pups start going potty outside at 4 weeks of age and are virtually potty trained when they leave my house at 8-10 weeks old.
I also start them in the plastic crates about 5 weeks old... so they are used to both wire and plastic crates at an early age. With this comes feeding separately. My pups eat 2 of their 3 daily meals in their crates. One meal is eaten in the big puppy pan together. I want them to be okay with another dog next to them eating... but also want them to learn that eating in their crate is okay too... makes them more than happy to go in their box!!
I am sure there is more that I do... but can't think of it right now!