Hey John:

It depends on what kind of flexibility you're looking for.  Themes consist of a series of template tags very similar to how WordPress template tags are used in WordPress themes.  So if you're comfortable digging into files and moving things around and comfortable with applying CSS you'll have quite a bit of flexibility.  But if you're looking for a point-and-click solution, that's not available. 

You can move any files you customize into a child theme (again, similar to how WordPress themes work) so that updates to the theme do not overwrite your changes.

If you open the default theme barebones theme files (the important code files are under the templates folder and the styles are under the styles folder), you'll likely quickly get an idea of how they are structured.

I hope this helps.