If you are set on a Largemouth/Bluegill pond, stock Bluegills at the rate of 15-30 for every Largemouth you put in the pond. This is for fingerling fish. Figure 75-100 LMB per acre so adjust your LMB/BG numbers accordingly.
so the simple math is
1/2 acre pond.
low side 37.5 LMB / 562.5 - 1,125 BG
High Side 50 LMB / 750 - 1,500 BG