I know that the Elijah Baley, Galactic Empire and Foundation books share a common timeline, but I don't know if Multivac, Lucky Starr, Nemesis, The Gods Themselves, Fantastic Voyage and others fit in the same universe or not.
Is there another 'big' Asimov universe in which several books and stories take place or is the Foundation universe the only one?
The Robots/Empire/Foundation universe is the only one where Asimov tried to join everything up. In addition to the books in those series, it's strongly implied (in Foundation and Earth) that The End of Eternity also fits in that timeline.
The robot stories (Donovan & Powell, and Susan Calvin) are (mostly) precursors to the Robots/Spacer novels, so they fit in too, and some of those do include a computer called Multivac, although that was a name he used in various places (eg in The Last Question, which can't really be said to fit).
I don't think any of the other books you mention fit within that timeline. Asimov did, after all, write around 500 books, many in contradictory universes, so it would be too much to expect them all to fit in. Many fans, me included, think he already went too far trying to harmonize the Robots and Foundation universes.
Nemesis fits in at the very start of the series, well before the empire novels.
The ship there is based on a very early hyperspace engine.
Nemesis was placed much later by Asimov as part of the Foundation mega series. It was mentioned in either "Foundation's Edge" or "Foundation and Earth" (don't have the books with me) that there was a legend of a sentient planet that talked to a girl. I believe it was strongly hinted that this was a precursor to Gaia.
I'm not aware if any those other books were placed similarly.
