This is a boring note-to-self post to serve as a reminder of how I did things. For what it's worth, most posts will be boring notes to self.
First permanent image uploaded. The process was as follows:
1. Edit image (remove a couple of distracting scuffs);
2. Prepare image for web;
3. Add to Squarespace.
Editing involved loading a PNG version of the image in Inpaint 5 (handy single-purpose app to remove unwanted stuff from photos), highlighting the scuffs and then pressing a single button to fix the image. Saved back as PNG, and then reimported to Aperture.
Preparing for web involved creating a custom export format (JPG, Q11 (to shrink file below Squarespace’s 20 MB max), watermark) and then dropping the file on the desktop.
Adding to Squarespace was the easiest bit: went to the Images page, selected add image and then picked the file from the desktop.