Chip, welcome to TreasureNet, glad to have you aboard!
You raise some interesting questions. Before addressing them, however, I have some questions for you.
1) Do you have a metal detector? If so, is it appropriate for seeking caches? Unless you are going to be dowsing for your caches, or digging based on some obvious signs and clues, you'll need a good, deep-seeking metal detector.
2) Do you know who Karl von Mueller, Deek Gladson or "Hardrock" Hammond were? If you don't know who these men were, you should read all you can about them. Here's a hint: Karl von Mueller and Deek Gladson were basically the same guy. The "team" of Karl von Mueller and "Hardrock" Hammond probably found more caches than any other guys in their day. Read von Mueller's books and you will gain much information about how to go about finding cache sites.
3) Do you have lots of patience and do you enjoy doing lots of research? Without patience and a love for research, you might not be suited to cache hunting. Finding caches is usually not easy. Very few people find caches without great effort.
4) If you have the patience, enjoy research, and if you have a good cache detector, you may be ready to circle around back to your original questions. If not, you may want to try a different type of treasure hunting.
There is no single best answer to your question. Sometimes learning about a potential cache site from a relative of a cacher is the easiest way to proceed...just start searching the grounds. Since few people are willing to share information -- especially about buried treasure -- you might have a long wait before you meet someone willing to talk about a cache that might be buried on their land. Sometimes the only way to get a clue is to read hundreds of obituraries, looking for these tipoffs: did the deceased have any heirs? Did the deceased's hometown have a bank? Did the deceased have any money to hide? Did the deceased own land? You will also need to ask yourself if the property is accessible? Is the current owner going to let me search the property? Do I need to have a legal document drawn up to cover myself and my discovery? Is the cache big enough to warrant my attention?
In my opinion, the best way to find caches is to do some pro-active research. Go to the library and read old obituaries, look for people who had no heirs, or no heirs in the vacinity. Look for people who lived or grew up during the Great Depression -- folks from that period seldom trusted banks. Check directories to determine if a bank was in the town where the deceased had resided. No bank, no place to deposit money -- except in a cache. And think outside the box. Try to think like the cacher. Try to determine where you would hide something, while visualizing the terrain and the location of buildings at the time.
Cache hunting is hard work and often frustrating. If you find a good cache, however, all the work and frustration will be worthwhile. I have only found 3 small caches in my whole life, I would not have been able to pay the bills if I depended on caches to support me. Others, like the men I mentioned earlier, supplemented their incomes with other things while they searched for caches. You may not want to give up your job or home or whatever in pursuit of caches unless you are independently wealthy or you can supplement your income with other things while working to find that first big cache.
The best places to do research: libraries, county/state archives, newspaper archives, historical societies, genealogy societies, universities/colleges, used book stores, antique shops, county recorder's office, and any other place that has information about people and places.
Sorry to have rambled so much, but your question leads me to believe you are just starting out and may not know some of this stuff. Good luck and happy hunting.