I am not an expert here, just want to share my little experience. Almost all fruit trees will benefit from cross pollination, even citrus tree. Some trees will fruit a lot heavier when cross pollinated, some just a little heavier. Depending on the variety, climate, and other enviromental factors.
Rambutan in my home country (indonesia) grow really big. I mean really big. I remember saw one about 20 meter in height and width as a kid.
Planting them one meter apart would be too close, unless you plan to trim them really heavy each year. It might not grow that big in Australia.
Maybe 3 meters apart will be decent.