1. No, I don't think so. I mean, the fact that Izumi is Ryusuke's bro's childhood friend probably wouldn't be that much of a barrier for him (at least at that stage in the manga, I don't remember how close they were at that point) but Izumi seemed kind of innocent...when she went to high school she got a boyfriend then broke up with and immediately had a crush on Koyuki. So, I don't think so.

2. I'd assume as far as Koyuki's and Maho's, that is, all the way. Why not? They seem to be just as into each other, it just wasn't expressed because they didn't have any of the barriers and obstacles that the main couple did.

3. Actually, after I had read about 18 volumes of beck and found that trailer whilst searching for ch 54, I was quite excited and put it on my list of Jap films to watch if I find it at a rental store. It looks like they did a good job. No idea how far they go in the storyline, though. Probably just the first big concert (Greatful Sound).

4 HELL YES!
Probably my favourite female character in a romance-tagged manga. At least, I can't think of a better one at the moment. She seemed a lot more spunky at the beginning, though. I'd have liked to have seen her interact with other characters like that more throughout the manga. Not acting like that towards Koyuki later in the series make sense and she was bound to mature but that spunky side of her was really cool too.

Oh, and:
2. Yeah, I was wondering what would happen to Sayako Glasses Girl and Kiyuki's friendship after that festival. Feel quite sorry for her and was disappointed when she simply stopped appearing. I guess that means their friendship is over with her probably crying for a while. Unless she did appear again, if so someone tell me where. I'm pretty sure she didn't.