I can't say exactly what kinds of plants to buy for your area, but I can lend some advice...

Visit some ponds nearby and ID and research what is growing in them. Plants growing in BOW's near you will tell you what REALLY likes your area. You might even find some to transplant and save some money. Be careful with transplanting so you don't bring unwanted hitchhikers into the pond. This goes for purchased plants too. Some that I bought had duckweed in them.

I have stayed away from most submerged plants as it seems that almost all of them grow in waters that are 6 foot deep. My pond is pretty small and an evasive submerged plant would greatly reduce my available water surface.

I have focused on the emergents and marginals with good success.

Pickerel Weed
Thalia Dealbata
Arrowehead
Common Rush

...are a few that like my pond and should do well in your zone, but double check.

I am currently experimenting with American Pond Weed (a submerged plant), but my crawdads make it difficult (impossible really) to get established on the pond floor. I have them in hanging baskets off the dock...we'll see what next year brings, but my hopes are low until the craws are greatly reduced. APW seems to be favorite for pond/lake owners and it is likely to be the easiest to manually remove if it gets out of hand compared to other submerged types.

I will be trying some lilies next year in the hanging baskets, maybe. I really don't want those getting loose in the pond however. Nothing like rolling the dice? lol

Fish on!,
Noel