this is an amazing validation of the pain point. sounds like you and I had similar experiences. we want to get to the point where people do not need to do this themselves.
For example, let the user put it the price of a house. That's it. With 0% down payment. Show them the graphs and the monthly payment (without taxes/insurance). In 1 second, they immediately have something in front of them.
Then, let them enter in a down payment, as they are doing so in real-time update the graphs/payments.
Then they choose 15 or 30 year, and keep adjusting parameters. They started simple but are slowly building up to see what makes a difference and aligning it with what they can afford.
At least, that's how I approached it. I want to see graphs/payment before I even have to tell you my savings.