For your suffix question moezy-chan, I'm quite confused myself. I remember how Syaoran/Meiling said that it was extermely intimate to say someone's first name. I would go to cultrural route, but then it would have to apply to Meiling as well
Though when you think about it, using suffixes are also a way of saying how close you are to someone, or if you have respect for them. In the beginning, Syaoarn just said 'Kinomoto' or 'you'. He wasnt very respectful to her, or his peers even. I dont think its in Syaoran's personality to use "-san" or even "-chan". Perhaps once he started to like her, he just called her 'Sakura', which is his way of showing that they've become closer rather than adding the suffix '-san' or even '-chan'.
To me, its most likely Syaoran showing they've become closer. If anything, I doubt he was insulting Sakura, he doesn't seem like the type to do that to people he likes.
Oh, I thought of another thing! I remember from statistics that Syaoran's least favourite subject was Japanese, so perhaps he's not as good as it as Meiling...?
I'm probably over-analyzing as well >.<