Curious to know your revenue model as you advance. Are you planning on 'referral fees' for presented loan offers? And would that approach threaten your appearance as source of neutral information?
I recently bought a house and used this[1] mortgage calculator, which was the best one I found. I liked how you can pivot from calculating on monthly income, purchase price, or a total monthly payment. An easy way to play with the numbers. Of course, since it's a simple calculator, it does require more manual input. I will say, though, it might be nice to have a manual mode with places you can input all those numbers a broker will throw at you.
[1] http://www.mortgageloan.com/calculator/mortgage-qualifying-c...