Those four cannot be Cylons as previously seen. They may contain Cylon consciousness in human bodies, or be as I said before avatars for a higher-state Cylon being. But if they were around as regular skin-jobs 40 years ago when Tigh and Adama first met, that would put Anders/Tyrol etc. as the same age. Anders was famous in the Colonies. You don't think anyone would have seen him on TV at some point and said "I know him from years back, he must be about 70 years old by now"?
Good points. The other thing to consider as well is that, well, the Cylons are machines. Very advanced ones, yes, but there's still the whole issue of them having emotions, souls, "consciousness" as you say, possibly being "higher beings" as you put it, etc. - how is this possible? Again, something which will be explained in Season 4 no doubt...
So along these lines, is it possible Starbuck is not a Cylon then? Simply a messenger or aide in everything? This wouldn't explain how she came back from the dead though... unless she hasn't...
... unless Leoben was right in Season 1. Before he was blown out the airlock he whispered to the President, "Adama is a Cylon." Granted this was no doubt to engage in some psychological warefare with her, make her doubt her leader, divide and conquer, instill paranoia, etc. etc. But what if he was right? And everyone assumed he was referring to Admiral Adama when in in fact that isn't the case - Lee Adama is the Cylon. Apollo. It appeared as though no one else saw Starbuck on Draedus at the end of the last epsiode, only Lee. Starbuck then spoke to Lee not through their headsets, ship-to-ship, but in a normal voice. Could it be that Starbuck is now in Lee's mind, just as Caprica 6 is in Baltar's mind? Of course this doesn't mean Lee is a Cylon though... after all, Baltar is probably not the final Cylon... but could Lee be the final Cylon? This wouldn't explain though how he had a childhood and his father would have remembered his birth, and so forth... But then again, we apparently know nothing about the circumstances surrounding the final five, what makes them special, etc., so who knows?
Just thought I'd throw that out there for fun...