If you can tell from what your app needs to do that you will need to go native, bite the bullet and learn one of the native tongues (Objective C for iOS or Java for Android.) Bell strongly advises that if you go the mobile route, pick iOS or Android and build for that first.
The first thing you need to do is talk to your loan officer and accountant to determine your total interest cost, net of the tax benefit, which will tell you how much your investment portfolio needs to earn in order to pay off the interest-rate charges of your mortgage.
There's also a Facebook award you can score when you link your Facebook account, if you're the sort of person who needs to tell the world what you're reading.
Can you create a business plan that starts with relatively less risky steps to help you analyze the market, find your customers, discover their needs and thoughts about your business idea, and then alter your strategy if your customers tell you to do so?