Fiber networks occur abundantly at all length scales in the biological and non-living worlds. Various applications of such fibrous materials require them to maintain their structural integrity. Hence, an accurate understanding of the factors affecting failure at system subscale is important. Since these materials are structurally stochastic, heterogeneity plays a major role in determining the dominant failure mechanism and affects strength and toughness of the material. In addition, most of these networks naturally occur as composites (e.g. in various types of tissue). Previously, we studied the effect of heterogeneity in the strength of the inter-fiber bonds on the overall network strength. In this work we study the effect of structural heterogeneity and network architecture, on the macroscopic strength and strain-at-failure. We observe that increasing the structural heterogeneity increases the strain-at-failure while the strength remains unaffected. Thus, we propose to use structural disorder of these materials to control their toughness. Further, we investigate the behavior of network-based composites formed by embedding spherical inclusions, rigid or deformable, in a fibrous network. A small fraction of inclusions strongly affects the network stiffness and alters drastically the microscopic deformation and failure mechanisms. This is due primarily to the confinement effect of inclusions on the deformation of the network.