While I'm still myself considering Nick Szabo the prime candidate from a knowledge perspective, possibly with one or two others in mind, here's something to consider.
The answer to #1 is actually irrelevant, because the design draft and even the final white paper had both been published far before Nick made the comment you are referring to here. The draft as early as August 22.
So while it's possible that Nick was Satoshi, he would have already known the solution.
Nevermind, I had forgotten that Nick edited his post and the comment was actually not made neither in 1998 as you said or in December of 2008 as the blog post says. Rather the post and comment is from April, giving him plenty of time to code up the solution after which Satoshi claims he wrote the paper.
As I said, there is a lot pointing to Szabo. What throws me off is how disagrees with Satoshi on certain technical aspects post-Bitcoin. It might be a genuine change of mind (for good or bad reasons), it might be a way to disguise himself, or it might still be that he never actually was Satoshi.
Well Szabo is almost certainly Satoshi or a PART of Satoshi. Wei Dai might be his "better half", but so private it's impossible to gain any real evidence on him (which is very Satoshi-like).
Another factor is Szabo doesn't really work anymore. How's that possible?
Do you have links on when/how he disagreed with Satoshi (assuming this is after Jan 2009?)? Would like to read them.
It's been awhile since this article was written, not sure "1998" wasn't a brainfart typo and was supposed to be 2008 (December).
What is the source for Szabo editting his posts? Wanna read that too, altho I do remember reading something about that.