Here's part of an old interview with Ron Moore which took place in July 2008. It includes questions that season 4.5 is supposed to answer. The line of questioning doesn't reveal anything about the final episode beyond whether or not certain questions will be answered. If you want to consider that being spoiled, then don't read on.
AS: The identity of the final Cylon, we will find this out?
RDM: Yeah. [Mo here: Answered -- Ellen.]
The origin and nature of the Final Four and how they're different from the rest of them?
The origin of the rest of the skinjobs?
What happened to Earth and what happened to the 13th Colony?
Yes. [What happened to Earth -- Answered. What happened to the 13th Colony -- partly answered or fully answered? The 13th Tribe, the Cylons, left Kobol and settled on Earth -- does that cover it? Tell me in comments if you consider the second part of the question fully answered.]
Who, if anyone, is orchestrating all of this?
Basically, yeah. I don't know if it's going to be wrapped up in a neat bow. The show has an answer for it, whether it's a satisfying answer, I don't know. [Not answered yet]
Will "All this has happened before and it will happen again" be explained in some way?
Yes. [I'd call that partly answered -- there have clearly been Cylon and human wars for hundreds or thousands years. Do you consider this question answered?]
The opera house?
Yes. [Not answered yet.]
What happened to Kara when she went through the Maelstrom?
Pretty much. [Not answered yet. I'm guessing she was a beneficiary of the kind of "organic memory transference" technology that the Final Five used, but we don't know for sure.]
Identity and nature of the "head" characters?
Yes. [Not answered yet. I'm guessing they're Cylon projections of some kind.]
Tigh and Six's baby, and whether that means Cylons can breed?
Yes. That's not a "yes" to whether they can breed -- the question will be answered. [Answered.]
The fate of Boomer and whether there are other 1's, 4's and 5's floating out there?
Yes. [Answered. Boomer, as well as Cavil, Simon and Doral (at least one of each), are all aboard the Colony.]
Yes. [Not fully answered, but it's not looking good.]