Sorry to hear about this accident and my condolences to all concerned.
A trick my boss taught me flying in Zim. If you are worried you are too heavy, take a small load and see how it goes. If you feel you can take more, go around, land and put some more in the plane.
Another tip is to pick a point 3/4 of the way down the runway and make a go / no go decision when you get there on the take off run. You should be able to tell if the plane is going to fly by then and hopefully you'll have enough room to stop if you feel uncomfortable.
The following may not be relevant to this accident but looking up performance charts in a bush flying scenario can be misleading as there are so many factors not considered in the charts. Surface conditions (sandy soil vs compact clay), runway slope, terrain, trees or power lines on climb out etc etc... I remember taking big loads out of short strips where conditions were right and visa versa.