We present a theoretical study of the effects of amphiphile microscopic properties on mesoscopic properties of their solutions. These results were obtained using an off lattice density functional method. We consider fused hard-sphere amphiphiles with a single hard sphere solvent. Mean field attractions are accounted for with a 1/R-6 dispersion interaction. Mesoscopic properties, such as the bending rigidity, saddle splay modulus, and surface tension, are presented as a function of the amphiphile hard sphere radii and attractive interaction strength. Detailed analysis of the work of amphiphile cluster formation with cluster size is presented.