Hi geoaspro, Sorry, I have not worked a lot with Spica, so I don’t know how to change it to a 3 column layout.
But judging from the site, I does not look like you have that much content yet. Would it be an idea to use a different template. There are many 3 column templates that you can use “out of the box” so to speak, so that you don’t have to modify, and possibly come up with more problems. Ja_Iolite for example, has three columns and has some of the same features as Spica. I think it is easier to modify a few colors than the colums and layout of the template.
Good luck!