We have a ruin near me that I was contemplating flying but it is an English Heritage site and they have posted notices banning drone flyovers and recording, I am not sure if it is a blanket ban with English Heritage but I would check notices and get clarification if I were you
Flight plans vary in detail according to who requests them.
For your purposes I would suggest:
Date of proposed flights
The times from start to finish of the whole exercise
The location (lat/lon and what three words) of the centre of the flight. and how big a radius around that centre you wish to fly within.
The maximum altitude you wish to fly at
That’s normally good enough for most ATCs but the organisation you will be contacting may want more - insurances, qualifications, aircraft type, colour of pilots’ socks …