you might want to add Special Days as well: these are public holidays, CPD days, etc.
and 4. yes…currently time consuming, we will try and add an import one day. We do not do Parent photos, but you could. Parents can also add their own photo, which few do in my experience.
One thing is missing is departments, which (as mentioned in another reply to another post from you) are used in assigning unit editing rights for units.
Also, before enrolling students, you will want to add your form groups/roll groups/pastoral care groups, and also check that the list of Year Groups (e.g. Y7, Y8, etc (as opposed to school years, e.g. 2010-11, etc) that come with Gibbon match what you have.
One more thing to remember is if importing from another school management system make sure staff who are also parents are not duplicated in your import. Eg imported as a teacher with one username and as a parent with a new username.
George