You can let them decide? Then follow agile principles to make sure they are delivering prototypes/features. Ideally you would get a grasp of what they need to

You can let them decide? Then follow agile principles to make sure they are delivering prototypes/features. Ideally you would get a grasp of what they need to do and some idea on how they need to do it. If you don't then you should hire someone that does, or who you can feel almost absolute confidence in. Then let them do the hiring. Just my two cents.