Does anybody know any online resource that lists strictly what is canon within the Star Trek television and movie series about Andor/Andoria?
As others have mentioned, looking up
Memory Alpha for Andorians will give you onscreen info only.
But then the books also tried to say Andorians have four sexes, and all we ever see on TV and in movies are two sexes, so I don't put much stock in non-canon Trek.
Well, it was Data, in the canonical episode "Data's Day", who mentioned that
"Andorians marry in groups of four, unless...", opening up the possibility for the novels to play with a more alien concept that two sexes only. Editor Marco Palmieri and the writers decided to take the route that offered the most different stories without clashing with (then-very limited) canonical Andorian facts. (Sure, they
could have gone the two-gendered route and been like almost every other alien race in Trek, but why not try something different?)
Very cleverly, two of the novel Andorian sexes are said to be outwardly male and the other two are outwardly female. So, with canonical appearances, there is really no clash. The ENT episode "The Andorian incident" gives us Shran, Keval and Thon, but also the more androgynous character Tholos, who seems as interested in Trip as he is in T'Pol. (Curious body language from Tholos in that episode.) In later seasons, we meet two quite different female types are presented in Tarah (who is taller than the males and quite aggressive) and Talas, who is Shran's partner and perhaps more feminine.
It also paid homage to some popular 1970s fanfic by Leslie Fish (the infamous filksinger), whose zines suggested three sexes for Andorians.