Actually, in ACF 5 there is a function to get all of the field groups and then using each field group you can get all of the fields for each group. The functions are not documented but they are acf_get_field_groups() and acf_get_fields(). If you search the ACF code you can find them.
In ACF 4 this could be done with filters apply_filters('acf/get_field_groups', array()) and apply_filters('acf/field_group/get_fields', array(), $group_id). These were never documented either, but if you search the code you will find them.
Yes, at one time the fields in a group were stored as post meta for each of the field groups. This was changed because it caused an issue when nesting repeaters.
In ACF 4 the version can be gotten using a filter as well apply_filters('acf/get_info', 'version').
I think the version number will be important to you, like I said, there is supposed to be a free version of ACF 5 released and knowing the version will be far more important since you’ll need to base what you do on that and not necessarily on if it is the free or pro version.
