Biggest issue you're going to run into with a 3" trying to do long range is going to be its efficiency. Whatever you do you're going to have to run Li Ion and you can't punch out hard with it. You also won't be getting 10 km of range with any sort of digital system within a suburb area due to Wi-Fi pollution. You also have to get above the house line to maintain a positive connection. Otherwise we're going to run into hard drop-offs.
If you really want to do long range and don't want to go big and it has to be an open prop then I'm going to recommend sticking with a Flywoo LR4 and a 3000mah Li Ion or bigger battery.