Depends a lot on depth of water as that has a big impact on water volume. I've recently fished 2 x 25+ acre lakes - both holding 1000s of carp. One is an average of 20+feet deep, whereas the other is only about 8 feet deep on average.
I would have no concerns about the fish in the deeper lake - the volume is more than twice that of the shallower lake.
You will obviously catch much less in your 20 acre - 100 fish lake, BUT the fish will be less stressed, better water quality (the most important thing full stop) and you will learn more and appreciate your successes more than on an easy runs water. My early experiences on a lake of 25+ acres with 35 fish, choked with weed gave me invaluable skills and understanding - a fast track apprenticeship if you like. Go for it!!!