Well the biggest thing you need to do is to answer the questions of: What do you want out of the system?  With that answered you get  focus which helps in the process of making it. Also don't forget to work out your base math for stuff before you start adding stuff to it like crits.


Secondly it seems like you're doing a D&D type setting which is cool and all. But my question is what does it offer or do differently from not only D&D but countless other derivatives