In terms of where to locate the park, Disney was a big early believer in a analytical approach. They hired SRI to determine the best location for Disneyland back in the 1950s. They came up with a amazing amount of operational and systems research that we use now. The big factors where climate, access to a huge population base, and multiple access to freeways.
When it came to Disney World, the factor where those, plus the ability to buy large amount of land before anyone was aware of it, and could drive up prices with speculation.
Disney has tried a number of different strategies in the past to make parks more accessible - including the idea of building a Disneyland on a boat, that would travel the world, and stop in various ports for months, before packing up and sailing to the next trip.
Most of the demand for Disney growth wise is international, with Brazil probably next to get a park.
In terms of line waits, there are two things at play - one Disney has realized that they have been leaving money at the table. Contrary to this article, the vast majortity of the excess demand is not single day visitors at Disneyland, but rather season pass holders in California. This is why they have jacked up the cost for annual passes a ton. I was listening to a podcast recently that postulated that as much as 45% of the daily visitors to Disneyland might be annual pass holders. Expect the cost to go way up - it’s getting close to double the cost of a Disneyland pass compared to a Disney World pass.
The other thing is that Disney is putting massive capital into the parks, to grow them. They just opened Avatar land in Animal kingdom, but the most exciting are the new STar Wars Land, Toy Story Land, Epcot overhaul, and marvel land in California. Disney will be adding a ton of capacity, but they are trying to raise ticket prices to offset.