Find the weak spots in my idea

Be an honest critic of my idea. I don't need support. I need to find the weak spots before I spend time and money.

Idea: [what I want to do, for whom and how it will work: 3 to 5 sentences]
Why I believe in it: [my arguments]
What I have: [time, money, skills, connections]

Do the following:
1. Restate the idea in one sentence so I can check that you understood it correctly.
2. The 5 most serious weak spots. For each: what the problem is, how dangerous it is (will kill the idea / will make it harder / minor) and why you think so.
3. Separate my arguments into facts and hopes.
4. Who already solves this problem, and why people might not want to change their usual way of doing it.
5. The cheapest way to test each of the 3 biggest weak spots within a week, without building anything.
6. What has to happen for the idea to work: 3 conditions.

Rules: don't soften anything. Don't make up statistics or market sizes. If a number is needed, tell me where to look for it. At the end, one sentence: what you would do first in my place.