Haha, lordy. Sprawl. Can't say I have too much advice to give you because of that, Drew, because that serial didn't have much of an audience, and it wasn't a funnel for all sorts of other series. I'm honestly disgusted by KU's exclusivity requirement -- its blatantly monopolistic, and for all of Amazon's claims that you don't have to join, indie authors really need to join to access so many of the readers Amazon has now trained to only read things for free.
The whole thing is a huge lawsuit waiting to happen. One's going on right now, but it probably won't succeed because there are three things that need to happen for a monopoly lawsuit to succeed.
1) Company needs to have a dominant market share (85% of self-published books, so check)
2) Company needs to purposefully be hurting competition (KU is obviously doing that)
3) The monopoly needs to be hurting consumers in some way (this is the line they haven't crossed yet; it might take years, but I'll be shocked if they don't cross it eventually)
Onto more practical matters: I'd give your audience a thirty-day warning. Mention it on the blog like you said you were going to, say it on Twitter and FB and wherever else. Then at the end of the thirty days, put it in KU for a couple months. See which one does better for you. Your plan sounds good, but I'd be wary of giving them a say in it if you need to get into KU financially. If it's really a decision you still have to make, awesome. But if you're asking them for input and it's all negative, are you gonna be cool w/ not putting it in KU?
About Corpies: I read it without reading Super Powereds, and I actually really enjoyed it. There were little references I wasn't familiar with, but they all really felt minor. And they were all explained in-text. (Like when the protag is talking about his sons, who go to a school, I was like, "Oh I bet that's a Super Powereds reference. I didn't need to read the books to figure that out, lol!)
No matter what, hope it works out for you, Drewster!