in a formal manner? no, but in reality yes.
in the late 3rd era (aka, the time during Morrowind and Oblivion) Talos was probably one of the most heavily worshiped deity's (probably only Akatosh was higher up), but during the 4th era they "pretend" hes not a divine because the treaty gave them time to rebuild.. but people still worship him, just not openly
all of them, you got to remember the whole "nine divine" thing is an imperial concept (as far as I know, no other religion reffered to their gods as the Divines), they are the Imperial gods after all and i think its the only pantheon that calls their gods "the nine" or "the eight and one".. alot of the other pantheons (such as the nord one) don't contain all of the same gods that are referred to as "the nine divines"
only person I can think of officially labeled as a saint would be Alessia.. however, people like Pelinal posses some saint-like respect..
not at all, they worship whichever divine they wish.. its a Pantheon after all, you don't just go "hey, i like Akatosh and you like Zenithar, get out!", they are all gods within the pantheon, they just each represent a different aspect of the world.. however, many people do worship multiple divines
no, they recognized him as a god from the very beginning (well.. he technically didn't exist as a god at all during Arena or Daggerfall, but he retroactively became one because Numidium shattered space-time again).. it wasn't until well in to the 4th era where they had to pretend they didn't..
i'd also like to point out, just because your an Imperial doesn't mean you worship the Imperial Pantheon.. just like you don't have to worship the Tribunal if your a dunmer, or the Nordic Pantheon if your a Nord (which is very true because in the game Skyrim, we see very little representation of the Nord pantheon.. everyone, and ever chapel seems to be devoted to the Imperial one.. Arkay doesn't exist in the Nord Pantheon as an example, and we see no shrines for gods that are in the Nord pantheon like Stuhn)
the religions in TES are not based entirely off of race.. they are based off of culture.. if you go play through Oblivion and Morrowind, you will find plenty of people who worship alternate pantheons..