firstly the aircraft you fly must be insured for $30mil( think its about 17mil Euro) third party property damage to fly in Turkish airspace if its a jet not sure for props.
Dont even consider coming into LTBA as you will not be given a slot due to congestion (read notams) alternative is Corlu 1 hr drive west.
as for services
celebi, havas, TGS are other ground agents
i have a contact in corlu celebi , friendly lady who speaks good english...if you want pm me for the details