http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=330504#Post330504 I think the pond will work. You may have some issues like I do with groundwater fluctuation levels. Definately try NOT to have an overflow pipe going all the way to the creek for the reason that you mentioned - water backing from the creek to the pond.
Give it a real good guesstimate on what will be the lowest water level in the pond. Taper the pond banks above that level at no sharper than 3:1, less slope is better because of you having to walk on the slope to get to the water.
Dig the pond deeper than you think necessary, you will be glad that you did. Shoot for 12' depth from lowest water level over 30% of the pond if you can - it will be easier for the fish to survive the winter and summer. I would not stock Northern Bluegills, but instead stock Fathead Minnows as soon as you have a couple of feet of water in the pond. Then 4+ months later stock Hybrid Bluegills. Stock 15-20 Hybrid Striped Bass in the pond too, but another half year or so after the HBG.
When you are digging the pond, rent or buy a 3" or 4" semi-trash pump. Keep pumping the water out as you dig - you want to see what you are digging.
Can you use some of the dirt that you excavate to build a berm around the pond to prevent flood waters from entering the pond, but not enough that you disrupt the natural flow of water across your property? If you don't, I'd bet that you will have Green Sunfish and possibly other fisn entering your pond with the flood waters.