If you wanted to tile different images for the background, what would be the easiest way to code it?

You can have only one background image for each element, so you have to nest several elements to have multiple backgrounds.

http://htmlhelp.com/reference/css/color-background/

Another way, if it fits your application, is to combine the "different images" into one single image - say using photoshop, and use the resultant combined image as the the main background image.

FYI, the use of multiple images as background will be part of CSS 3. See the CSS 3 Backgrounds and Borders Module Working Draft on Layering multiple background images. But it will still take a while before browsers will have implemented CSS 3 (Safari already supports multiple background images).

What size would I make the canvas?

Ay, there's the rub.

Good question! I have not used background images for ages (only colors), therefore I do not have handy bag of trips to dig into. Also, I would think that the number and size of the images would be a consideration. Perhaps someone who has been using background images frequently may have some pointers for you.

I'd say it depends on the image. Since minidiapolis wants it to tile, 1 tile big would be the obvious choice. How big that is... well, I wouldn't know.