You made some valid points. I must say that I used "Vader missing Padme" because I saw that on screen - subconsciously I borrowed that from the movie, without letting my imagination to rewrite the story from the scratch.
Vader hating everything, including Padme for her "betrayal" should fit that character, too. However the latter SW movies tried to portray Vader not as 1-dimensional character as Palpatine (who could sing that retro song: "I'm such a cold bastard and I feel good with that, no doubt!", pure evil), as "there's good in him". So in my version Vader wants revenge on Palpatine - he's not just "power crazy", wanting to become "number one" because it's cool. Revenge for what? For loosing everything. This goal isn't against his way to the Dark Side - after all, he's fueled by hatred - even if it's hate to an evil person such as Palpatine is. This goal still isn't against his way to power - kill the old guy and get the whole Empire for yourself, to make up for what you lost. Makes sense?
About Annakin to Vader transformation - again my imagination followed what I saw in the movie, this time it was Obi-Wan. Kenobi's words give a feeling that Vader's inhuman behavior/morality is due to the fact that he's a cyborg now. So I imagined that his final step into the Dark Side (which includes getting new name) occurred when he was "transformed into machine". It has such "poetic" meaning: machines have no feelings, no mercy, no remorse. I even assumed - before I saw ROTS - that Vader will be instrumental in murdering the last Jedi Knights, i.e. he will personally slice the last most powerful Masters with his lightsaber (perhaps with a little help of Palpie in the hardest cases). I wanted to see Vader fighting in that armor, showing his superior powers to his former brethren. That was said before: "he helped the Emperor to track and kill the last Jedi". We saw him killing the Younglings - as far as condemnable is this evil deed of killing children (ie. requires you to be a real SOB), this is not a challenge in terms of using saber/Force in fight. Give this man some worthy opponent, some real challenge, not some dirty but "easy" job!
What do we get by this? - the Jedi would finally witness (on their own skins) how mighty is the Chosen One - and we could see it, too!
In the movie we only saw his evil side - not skill/power itself. We could argue that he demostrated a part of his prowess during the fight with Obi-Wan, but still...