No difference whatsoever, in Ukrainian there are several words for "and" purely for the purpose of sounding melodic.
Actually, we also have "й", yet another form of "and". We use these different forms so that the phrase rolls easily from your tongue, with no vowels or consonants clashing.
consonant-consonant: брат і сестра (brother and sister)
vowel-vowel: Олена й Олександр (two names)
vowel-consonant: : мама та тато (mother and father)
Haha, well, you know, sometimes when we speak we ignore this :) For instance, "мама і тато" is definitely more common colloquially (but that's because та тато in a row sounds a bit funny) , Олена і Олександр is possible, people say that, although I wouldn't normally do that, sounds like chewing butter, "а-і-о" one after the other.
But some, of course, you would omit naturally, if, let's say, the word itself ends with "i": коні і коти (horses and cars) sounds retarded to me --> коні та коти
And for poetry its very important, makes everything pretty ~
What do you mean? If you mean the ending (один/одна/одне) then yes, because in this case один is not simply a number but something closer to an adjective or a posessive pronoun, at least as you see the endings behave absolutely in the same way.
один кіт <-> мій кіт
одна сестра <-> моя сестра
одне місто <-> моє місто