Plus completely new procedures for operating in artificial gravity, safety measures, prototypes, startup, tests, exercises, docking procedures, ... Soon we are talking about big money. If you want to move inside capsules you need to balance and deal with vibrations etc.
There is a difference between a quick test and a year long health impact study. Those passengers need to be fed, supplied erc. Youd have to put the whole of ISS on a tether.
