I just started (like REALLY JUST started) and this is all good information.. I think once I get a few more under my belt, I may try to do something that's not in the middle. :-)
I mostly start from upper left. Sometimes (but it's very rarely) I start from the middle. It's kinda weird for me, because I used to my upper left. Why I prefer this way? Because I don't touch parts which are already made.
And when I start from middle, I have this weird feeling that I'm destroying my beautiful crosses with my fingers.