I don’t know what your intentions are for the pond but if it’s geared towards quality bass fishing I would try to get at least an acre. If you just want something to catch a few bream or catfish and supply a watering hole then you will be ok with less. I definitely would pay someone reputable to do the work. I have a neighbor that tried to go cheaper on two cattle ponds. One hasn’t held water for a full year in the past 10 years and the other had a dam failure about 2 years after he built it. He paid someone to fix it after that.