1. The center of the front wall may or may not be a good spot for the sub. The only way to know is to try it out.
2. If the sub vibrates, and that vibration is transferred to the CC, it could have a sonic impact on the CC, or it could cause the CC to rattle against the sub.
Lombardi said it:
Perfection is not attainable, but if we chase perfection we can catch excellence."