Is there a checklist or some stats that anyone has used that gives a comfort level to getting to a minimum valid product?
I'm a lone startup ISV and find that I need to take extra effort to mistake proof without another person asking quesitons and validating my thoughts. How do those that have an idea for a solution get to that comfort level while they go about building it?
Have you done a round with beta testers?
You need to get the product in front to as many eyes as you can.
Then, use their feedback to fix any bugs and improve its functionality.
Stefanos is on the money there. There's nothing better than watching people actually use a product and asking them what they like and what they don't. Sometimes you have to learn to decode what they're actually saying, but it's invaluable. If you can't do in-person testing, have them test at home and submit issues to something like ZenDesk and feedback to UserVoice (where I work - ask about a discount if you're interested).
Agree with Stefanos and Evan, there isn't a checklist or guideline that will be as useful and accurate as a beta test and the feedback you get from it. I am currently setting up my application for a beta test using Prefinery's service... they have a beta management service that works very well:
http://www.prefinery.com/ Good luck!