Wow, thanks for the quick and thorough answers!
1. The calculator looks good, but doesn’t clear up what is the recommended size mentioned in the instructions (pretty sure it’s 21×21″ though). Also I forgot to mention: the calculator shows both X and Y rails as the same length, but the cut list shows the Y rails 0.2″ longer. Which is correct?
3. Crap, if only I’d waited a week or two. Stainless would be pretty cool.
7. Ah, I hadn’t thought about pre-drilling at an angle; I just went straight down.
8. Hmm, I didn’t realize they were different size. That would probably be a good thing to add to the instructions as well. Pretty sure I used the correct one; the coupling nut fit into it perfectly.
9. Also didn’t realize they were different size. I probably have the wrong one on, as it slides right in. :'(
I understand completely about not having time. I’m pretty handy with WordPress, so if you’re fighting with anything I may be able to help.