Been there and done it. The pond was built first and extra soil was used to build house pad next to water. Bski has done the same you might look at his pond thread, he has documented the entire project from start(same place you are at now asking buy or build questions)to finish. I would not write off an existing proven pond if the price is right it may be worth checking for silting issues. Building a 8.2 acre pond can be expensive depending on the topo of the site etc. Good luck
Rocky