scaling image in page header

When I type the class into the section metabox. Can I just type bare text ie: bghome ?
Or do I have to type .bghome?

Just the bare text.

All of the dev I have done todate using GP I haven't used sections. So a bit of a learning curve.

Is using sections exclusive. That is, can I have a regular page but insert a section if needed? Or can the sections switch only be on or off?

They can only be switched on and off, but you can make a section look like the regular page with the settings.