DC, I forgot to note that after I get my story in order, I will renumber the chapters to get rid of the 8-a, 8-b, 8-c numbering. I don't much care for the 2a-2b-2c thing either, especially if the sub-parts are very short.
I use single spacing because I'm so used to it, but even in my personal letters (yes, I still write them) I'm now putting a blank line between paragraphs a la fanfic. I use Times New Roman 12pt because, again, it's what I'm used to. Like you, I also end chapters when there's a logical break point and it's time to change scene or POV. I've posted chapters of 3000 words or less because of that. And I try to keep both prologues and epilogues below 2500 words or they look like chapters instead of a setup (the prologue) or the final wrap-up (the epilogue).
There have been times when I'll go back to my older stories and read the feedback posts. It's nice to remind myself that someone liked my story enough to tell me.
