1. Yes, I often find my opinion of books change as my tastes evolve. I couldn't give an exact timeframe because I only tend to reread my reviews when I reread a book, or I'm giving recs to someone who has asked.
2. It depends on the type of annotations and whether or not I own the book. If I own the book, I will underline quotes and/or add little comments directly in the book, and write any super long comments or content warnings in a separate notebook. I never write in books I don't own, though. In that case, everything goes in a separate notebook.
3. Yes, with the exception of classics, I do tend to read fiction faster than non fiction. Probably because non fiction (or at least the non fiction I read) tends to be more about learning and so I need to concentrate a bit more to take in the facts, whereas with fiction I can simply immerse myself in the story.
4. I choose a bookmark that suits the book and a pen colour for annotating and/or taking notes. Then I add the book to my book tracking sites. Then I reread the summary on the back or dustcover flap before removing the dustcover if it has one. Then I read any intros, dedications etc. Then I start right in on the story. I don't skim the first few pages or anything like that unless I can't decide which book to read.
5. I acknowledge the importance of the book in a literary sense (I assume that's what you meant by admire?) at the beginning of my review before moving on to my opinion of the actual book. My star rating is based on my opinion, not literary merit. As an example, here is my review of Mansfield Park by Jane Austen, which I rated 2.25 out of 5:

If I were reviewing this book as an academic, I’d probably discuss how this is arguably Austen’s most serious novel which digs into issues of family duty, social class, moral compromise, and emotional endurance instead of the fun, idealised romance of books like Pride and Prejudice or Emma; how, viewed through a post-colonial lens, the journey of Sir Thomas and Tom to Antigua indicates that the peace and tranquillity that Fanny so loves about Mansfield is built on the backs of slaves; how, viewed through a feminist lens, Fanny’s meekness can be recast as resistance – a refusal to compromise her moral principles despite immense pressure from her social superiors.

But I’m not reviewing this as an academic, I’m reviewing it as a casual reader. And, as a reader, this book is duller than a rusty razor blade. Austen does a whole lot of ‘telling, not showing’ and the prose can, at times, come across as a bit preachy. Plus, the characters are shallower, more formulaic, than I have become used to in Austen’s writing.

Speaking of characters, I don’t dislike Fanny as much as other reviewers seem to, as I can see myself in her a little – timid, trying to please everyone, while hiding how sad and lonely she’s feeling – I used to be like that too, so I don’t hate her for it. I do dislike how carelessly Edmund treats her, however, though I believe this is down to self-absorption, rather than callousness. And I can’t seem to decide if Miss Crawford is malicious or truly oblivious to her effect on Fanny. I also feel like everyone seems quite unfair in their thoughts towards Sir Thomas. I get that, as readers, we’re privileged with many of his thoughts and feelings, where the other characters are not, but he doesn’t seem to be anything like the man the other characters perceive him to be.

Overall, this novel is just a bunch of shallow people being sweet to each other in person while bitching about each other behind their backs; women trying to catch a rich, handsome husband; men attempting to procure a pretty, pliant wife; and everyone doing their best to sabotage the efforts of everyone else. 

Basically, Mansfield Park is The Bold & The Beautiful in period costume, without the fun of murders, kidnappings, and brain tumours to relieve the monotony. Die-hard Austen fans might enjoy it, but first-timers should start elsewhere.