Joe, those "rules of thumb" about watershed ratios vary pretty wildly across the country. However, you being that far east in Missouri gets you to about the 5 acres of water shed per acre of pond contour in the guide.

I believe you should be fine, except for extended drought periods. (When nobody's pond is fine.)

Do you cut and bale your pasture, or does it have grazing livestock? Manure will fertilize your pond as it washes in. Probably not too bad at the start, but it will become more of a problem as your pond matures.

Also, since you should have fall rains coming, you need to get some groundcover established around the pond ASAP. Your bare ground that is showing after construction will try to run sediment back into your pond and start filling in your deepest spots. You can search the forum for best groundcovers if you haven't already started your plantings.

Congrats on the new pond!