Mainsite isn't well suited to general feedback. We have a class of questions which are Reviews. Most of the guidance we have around it is geared at homebrew review,† as that is the question type we get the most and which mostly works on the site. What's needed for them to work, is clearly defined goals which expertise can discern whether is fulfilled.
This is where, I think, the type of feedback you're looking for comes in. There are probably good questions which can be constructed around the goals of your system, but it's gonna be virtually impossible to answer without experience with the system (or a lot of expertise with similar systems). I'm not sure the effort (and likely unanswered question) will be worth it to you.
For general (less qualified) feedback, you want a space closer to traditional forums. We maintain a list of RPG forums here and we also have our own general chat. Among other topics, sharing, chatting, and giving feedback on creations is certainly supported in there.
†: See How can I ask a good homebrew review question?