As terrible as it sounds, I never really cared for Towa so this will likely just make me even more interested, sorry 'bout it
They're still very young and are all working on themselves as idols, so I don't think this will hurt them from a professional point of view. Also, I think Akari's graduation from Momoclo was a pivotal moment for the group, and this could possibly be the same for TakoNiji. It will just be interesting to see how the group dynamic changes since this is the first center/red figure to graduate from a major (although they're still indies) Stardust group.
She seems happy. She might just be putting on a brave face, but she seems confident in her decision. I'm surprised that the new leader will be Kurumi, but she stands out the least to me and I think this will definitely help pull her out of her shell more. I look forward to seeing where they go from here.
Also, according to the article, they will appear in a new commercial for Lotte (limited to Kansai) and the title of their next single will be "Zesshou! Naniwa de Umareta Shoujo-tachi."
That is a very good question. I assume they'll just leave off the last letter, maybe they'll all jump into the last 'a'? They currently don't have any events scheduled (to my knowledge) until mid-July, so we might have to wait until then to find out.
I could see it as Saki shouting the "I" and "A" at the end. Then letter rotation goes back to normal. This way no one has to shout a letter in consecutive turns.