Thanks for the query.
Event object format itself is fixed, it must be simple JSON without any nested properties.
However, other than mandatory fields like _type, _triggeredAt, _uploadedAt, _deviceID, the application developer is free to choose any number of fields. Field names should be in ASCII and supported field values are of JSON number, string, boolean or array. Array values must be of JSON number, string or boolean.
Yes, definitely! That's what analytics are supposed to be. Please check above answer for further details.
For iOS, please visit http://documentation.kii.com/en/guides/ios/managing-analytics/flex-analytics/
By the way, your keyword to searching analytics related docs inside Kii documentation is 'flex analytics'.