If you want to holdover trout (trout that make it through the summer) that will reach large size, you need the following:
Water that is well oxygenated and will not exceed 68 F. in the summer. Low 60's is even better. You also need to feed them a good quality commercial artificial feed. Keep in mind there are unstratified ponds that have cold water in the depths but most will have issues with that water becoming anoxic later in the summer. And it's doubtful the trout will come up for artificial feed much before they expire.
Smaller is actually better when it comes to a trout pond size as it's easier to keep cool, and doesn't require as much well water to do so. My trout pond is 88 by 59 feet and only about 10 feet deep in the center, but has steep sides to keep warming down. Even running a diffuser on the bottom center during the hottest part of the summer (highs in the 90's) my pond pretty much stays at 62 F. from top to bottom. I run a well at 45 gpm 24/7 through late spring and the summer into early fall. The overflow goes to my larger warmwater pond or bypasses it depending on what I want to do. Shut the well off
Believe it or not my 1/10th acre pond size is plenty big for enjoyable fishing.
In an earthen pond about 12 lbs. of trout per gpm is a rule the Brits use. That of course would be your final pond weight.
Btw my well water temp is 51.6 F. and it coincides with my mean annual ambient air temp of 52 F. In Wisconsin your ground water can be in the 40's depending on how far north you are. Could allow you to pump less well water.
