Kre
Some figures from the last flight I did on a 75 (Pax config aircraft; don't know about a Cargo config)
TOW = 110.5 tons
Payload = 20.5 tons
Fuel Burn = 23.3 tons
2550 NM sector, approx. 6 hours sector
Takeoff from a 2200m Rwy
Aircraft: MTOW = 115 tons; OWE = 61.5 tons
Works out, roughly, 3.9 tons fuel flow/hr (which sounds about right as we were close to MTOW of the aircraft). As a general figure for "ball park" calculations we use 3.5 tons Fuel Flow/hour. Would say that performance wouldn't allow for much more than that. Fuel at end of flight was 5.5 tons, so you could fly for another 20 or 25 mins before you start entering on your final reserves.
About your Rwy of 1800 m, have a suspiction that is going to greatly limit your performance and payloads you can eventually takeoff from there but I'm not able to offer any data on that right now.
Good luck with your business plans!!!
Zero