This is how I approached this problem-
My takeoff run is limited. So, depending on my configuration I calculated the maximum possible velocity I can attain in my groundroll. I assumed that at the end of the run my lift should be greater than the weight I want to carry. So I computed the lift I generate at the end of the groundroll. I got the CL value from xfoil for my angle of incidence. Would this method give me a rough estimate of the total weight my plane can carry?