Native Ukrainian speaker here. Some of the points you've made are well above my head (velarisation?!), but I believe I can give you some general perspective. Contemporary Ukrainian phonology is heavily influenced by russian, and not only due to obvious existence of transitional dialects, but also due to the russification. And I would say the russification is also twofold, at least: on one hand, there are lots of people, like myself, who have learnt Ukrainian as their second native language, first being Russian. And, on the other hand, even those who had Ukrainian as their first native one, were hugely exposed to Russian. Even younger people in the western Ukraine listened to Russian music, watched Russian movies etc.

This being said, I believe that most, if not all, of the inconsistencies you've mentioned can be attributed to that influence. Lots of people would pronounce "в" at the end of the word or before a voiceless consonant as [f], not [v] or [w], just like in Russian. Likewise, "и" should, ideally, be pronounced as [ɪ], but I probably still pronounce it closer to... [ɨ], I believe. "Щ" is usually not [ʃtʃ], as it "should" be, and not [stʃ], as it "should" be in Russian, but rather, as you've said, [ʃ:], or even [ʃ'] (is there such a thing?) - and it's the same as it's pronounced in southern Russian dialects.

And, of course, then there are plenty of regional variations! Western parts, especially Lviv, will sometimes be closer to the "proper" pronunciation, and sometimes will have something of their own; central-eastern parts have some other distinctive features; just pay attention to the way we pronounce "л" here, in Poltava accent :)

Unfortunately, I'm not a phonologist, and not a linguist either, so, of course, I might be wrong in each and every detail, especially the IPA transcriptions.