If President-Elect C. Thomas Howell wants to set up a website for the transition, it’s not much different than naming cabinet appointments before the inauguration, which happens often. It’s not really all that presumptuous if the man has just been elected to the office.
I don’t remember it being done by either of the Bush’s or Clinton, and CERTAINLY not 3 days after they were elected. Their first press conferences came mid December & then only a brief 15 minutes of speech & no questions.