I would suggest that it be just a little deeper to accommodate the winter temps (8-10'). Ponds often must be more than just holes in the ground, so it pays to do your homework. Most ponds need to be sealed, unless they are ground-water ponds (which often have fluctuating water levels). You will need to know your watershed area, and then have a plan to seal the pond to drainage which will depend on your soil structure. The overflow must also be planned to avoid damage to your property and those downstream. Our first pond was the best investment we ever made! We have many memories with family and friends that were made around that pond. We look forward to many more.
