Everything depends on your goals. If you want a nice catfish, bluegill and some bass pond, a 2 acre lot may be ok, depending on the lay of the land.
On a 1.5 acre lot you could probably get a one acre pond.
There are always issues when you dig but just identify underground stuff. Some of it may be able to be rerouted.
Ponds can definately affect neightbors. In the city or suburbs, they can also effect your Insurance rates, taxes, resale values, etc.
Yes, you probably should look for a bigger parcel of land. I would want to control all of the necessary overflow area to make sure my neighbor up the hill didn't put in his own pond or do some terracing that cuts me off from needed overflow.
