In the end, you just need to be able to find enough people who want to go (there are plenty) and who have the money to pay for the trip (Elon hopes to bring down the cost to such a level that someone selling their home on Earth could afford it in many cases - like $500,000 to move to Mars).

No. Unless Musk has a stupendous trick up his sleeve, this is a unavoidable problem with the whole enterprise. Hard as settling in the new world was, it was tremendously easier (even at the time) to settling on Mars. The best chance for a Mars colony would be an extractable resource that makes it economically sensible to support a non-self-sufficient outpost (i.e., try to become Edmonton, Canada). But there's nothing analogous to oil. The most promising natural resources in space are asteroids.

If you look at how many signed up for Mars One that shouldn't be a problem.