Sora has illusion powers, according to her promotion record. Also TBH I’m not sure her true form is Cautus either. Executor mentions he has a distant relative that has illusions and a “great musical talent”; assuming he’s referring to Sora then she’s probably Sankta.
Yeah, but for the reasons Hitomi mentioned in the anime. What makes this ship forbidden love isn't that they're both girls in general, but that they're Hitomi and Madoka in particular. Hitomi, return Homura her gf, before she makes you regret it!
There is new dialogue and one (non-combat) side quest that appears in the main game. It gets a bit awkward when you meet a character you already murdered in the side story.