Most of these should be `ConfigurationItem`s, rather than regular constants.  If you're not familiar with configuration items, you'll want to look at http://docs.astropy.org/en/latest/configs/index.html#developer-usage

The general guideline is that anything the user may want to mess with should be a configuration item, whereas something you intend as a constant for internal use in the package can just be a regular module-level variable.