First most important thing, і works for connecting nouns and adjectives as well as sentences, та and й work only for nouns and adjectives, and a is only for sentences
In this case (connecting sentences) basically, when you want to connect two similar sentences use i, and when they are contrasting or opposing each other use a
Я тут, і ти тут (I am here and you are here)
Я тут, а ти там (I am here and you are there --> has a flavour of "I am here while you are there")
no it should be there. I'm not even sure that Ukrainian has any silent letters. I could be wrong though so don't quote me on that, as there could be some obscure words I'm not familiar with
The Ukrainian ь is not exaaaactly silent, but it doesn't have a sound of its own; rather it modifies the previous consonant sound. Also, й is not silent, but it does have a very subtle sound, especially at the end of words
In russian at least, й changes a sound to a diphthong. That means it changes "a" to "ay" or "o" to "oy," etc. I'm pretty sure it's the same in Ukrainian.
Would you use "Ви", the polite form of you, towards adults to whom you are close? E.g. your тітка or дядько...
'Ви' is used predominantly in those types of situations. For example, I was born in the 80's and I call my parents 'ти' while most of my peers and older generations use 'ви'. I also, would like my nieces and nephews to call me 'ти' just because it's less formal and make me seem more approachable :) I believe the current trend in Ukrainian language is for people to use 'ти' much more often especially with close relatives. If you're ever in real life situation where you're not sure which one to use, use 'ви' and the other party is sure to give you suggestion to switch to 'ти'. Hope this makes sense :)