My favorite material is 6061 T6 aluminum. It's strong, lightweight, and easy to work with metalworking tools/mills.
Another option is Plexiglas-G, which is easily cut on a laser cutter, is lightweight and reasonably rigid, but not as strong as metals.
Motors are typically used with gearing, because tying a wheel directly to the output shaft is likely to spin the wheel way too fast, which would give you uncontrollable speed if it worked, but it won't work, because the torque will be too little to effectively accelerate the load.
5A may be a lot or a little depending on the voltage, and the weight of the 'bot it's moving.