I think your focus will depend on how you'll approach your development.
There's the rapid prototype method where you build small itterations and get regular feedback on what was fun, what was jank, and opportunities for potential.
(You'll want a wide variety of playtesters who want to feel clever at giving you unique well-detailed reports. The appeal of an advice-giver being considered noteworthy as they stand out from their peers can be incentive enough to want to give you value.)
If you follow a waterfall model for your project and have a solid idea of exactly what you want to craft, feedback is more observational and scientific.
(You'll have to devise all the components of your project yourself: UX, sound design, use of mechanics and how many times a player will attempt something before they give up, etc... and measure each one in a metric that's meaningful to you. You can get reviewer engagement if they feel that they've been given a challenge. And a 'try to break this game within a stated limited scope' can be just the thing if you believe your potential playerbase will all be trolls.)