Turf is on the appstore. Learn more at turf.life
The best feedback comes from a prototype people can see, touch and use. I like to start with something that obviously looks quick and dirty so people don't get hung up on the colors. This is for flow and usability.
Once you've nailed the features you can start making the product beautiful. Every product (especially software) should be a pleasure to use. For all the time we spend on the computer it ought to be beautiful.
Build and test is a never ending cycle in development. The trick is to give the appropriate importance to the feedback you get. It's easy to ignore feedback you don't agree with, think is trivial or too obvious to mention.