Speakers first. You want to mate them with complementary components. While given whatever speakers you choose it is most important to mate with appropriate amplification... the preamp can maters. For instance if you get hyper detailed speakers... you don’t want a lean hyper detailed preamp... mating is very important.
Tube preamp, definitely. This is the component that is really largely influential on the musicality and naturalness... get this one wrong and everything will not sound right. So choose a good tube preamp.