Heavy motors need large wing areas, for example, but large models need more power. A less powerful motor should not be used in a large model regardless of weight - pick a different motor if you want to build that particular model. A small model should be fitted with a light motor to keep wing loading under control. Be aware of design factors which may limit a model's durability. For instance, wire booms have a tendency to bend and break in certain crashes.
Tail fins are inherently vulnerable to glancing mid-airs and general crash damage.
Fuselages tend to break between the trailing edge and the tailplane, and need reinforcing in that area. Greater spans impose too much drag for all but the very best .15 to drag around at a good speed, although they do tend to turn tighter. Smaller models tend to be faster but less manoeverable. Also, large models are more adversely affected by wind, and vice versa. If you're in a windy area, don't go above 32 inches wingspan.