20-30 acres is a pretty large lake. In many states, the regulations are fairly simple to build the small ponds (appx. 1 acre) like those of many of the people on the forum. Moving up to your size is not just a change in scale, you probably will run into a whole tier of extra regulations.
For example, you will be impounding enough water, that if your dam breaks during a big rain event, there could be loss of life downstream. Lots more regulations when you get into that class. Also, for a 30 acre lake you are most likely going to be damming a stream, or at least an intermittent stream. That probably gets you into federal Corps of Engineering regulations. Further, with that size of lake you may need to secure water rights to impound that much water. There are several places in the Western (drier) states where 100% of the water rights are already allocated. I don't know about the rules in your target states.
Any chance you could get a person with regulatory experience on your board, or at least get them as a volunteer consultant? I think having that type of person might stop you from wasting time following attractive leads that cannot ever be completed due to some regulatory road block.
Perhaps find a property with an existing "ugly" lake of the proper size? (A large, attractive lake will probably already be owned by a wealthy individual or a commercial venture doing a development.) You might be able to drain and renovate an ugly lake to make it attractive and exactly fit your needs.
P.S. I don't understand this part below. Why does elevation matter to people with prosthetics? My father was an amputee (one leg, above the knee) and he lived at a much lower elevation. (Just trying to learn more to help out other people in need.)
They made sure that our standard location had to be above 2000 feet to accommodate those with prosthetics.
