First, thank you so much for taking the time to look at my site and share your feedback. Very helpful, and much appreciated.
After a couple of hours (I’m new to this, remember) of going through the code and experimenting with different margins, I found the solution to the “big problem” you pointed out.
It turns out the Amazon showcase widget was exceeding the width allowed for column3, pushing the whole thing way down the page. Which is upsetting, since I thought the baskets were probably the funniest part of the page. Is there a way to set the width of specific widgets using CSS, or will I have to play with (and break, most likely) the code for the widget itself?
As for the centering problems, it turned out this was caused by an incorrectly sized background image in column3. Everything seems to be nice and symmetrical now.
Thanks again.