1-> Yeah, pretty much. But it still doesn't make sense that someone as cruel and vengeful as Remilia supposedly is wouldn't do it anyway. She looks the type that makes her own rules, whatever the game.
2->Yeeaah, maybe I overstepped on that one. But I never really felt that Kanako looked like someone that could kick Suwako's ass, or that the very own Suwako ever made justice to her story as Misaguji-sama.
3-> I'll agree on the Reimu/Marisa fight but the more I look at IN, the more I feel like none of the characters there have actually anything to do with the rest of the world. Remilia, Yuyuko, Utsuho and even Kanako were real threats and have their own place in the plot for that. Kaguya is just... there... and then everyone decides to kick her ass because she looked at them funny. And after the game they're just there once again. It feels like those people are there but don't really have a place in the whole setting, with the possible exception of Keine (also: Yes, I know they're aliens, but Morya Shrine is as well and doesn't feel that way)
1) cruel and vengeful? After being defeated, Remilia visits Reimu (as shown in both endings, and mentioned in EoSD's Extra Stage), and canon *coughSSiBcough* tell us that Remilia is overconfident, prefers melee to danmaku (shown in SSiB as well) and yes, does whatever she wants to at the moment.
2) this can mean two things: one, Kanako won a fight against Suwako (by merit of superior strategy, or power alone, or adverse conditions regarding Suwako's abilities or the army of the place she was running, etc.. dunno.) one time, but may either lose or win again in a future fight (though in the first time, it seems that there were armies involved, and Kanako has crippled Suwako's army's weaponry by making them rust). Or two, Kanako has a large enough advantage over Suwako, meaning that this matchup is really in favor to Kanako (thus meaning that Kanako, due to such overwhelming advantages, has considerably better chances of winning, and/or that in a series of direct duels she would have more wins than losses). Not that Suwako is to Kanako what Ran is to Yukari; one example that I could use for comparison is Suwako being a shark, and Kanako, a lion. And they're both on land.
(since I mentioned Kanako interfering with Suwako's army and later having acquired the Moriya Shrine by "right of conquest", Kanako's abilities may, or may not be more focused on support rather than single, direct combat and thus, giving way for a third option. If this is the case, Suwako could even have a favorable matchup and not wanting to reclaim the shrine due to lack of interest. Anyways, I don't have such answers, but so far I don't have reasons to deny that Kanako had the ability to defeat Suwako back then, whatever her means and/or conditions were)
3) the plot of IN mentions that the youkai are affected negatively if the moon doesn't grow fully (which it doesn't do, because Eirin has replaced Gensokyo's moon with a fake one that doesn't grow full because this is the requirement needed for lunarians to travel to the Earth, and Kaguya and gang are willing to avoid them. They just didn't knew that Gensokyo is hidden well enough for the need to cut out the lunarians' way from the Moon to the Earth, however Eirin was right about taking safety measures; even after IN, moon viewing ceremonies are held in Eientei in order to magically avoid the lunarians' eyes, or ears..); most humans wouldn't notice, but the youkai do, and the youkai and humans are mutually important in Gensokyo (since if they don't fight themselves, their powers diminish and they become more vulnerable to outside threats.. such as Kanako -- even though she attempted to conquer the Hakurei Shrine because she cared for the balance of power based on faith. All your faith are belong to us.).