Hi Mike,

Do you want to start again and build a fully new control box or re-use some of what you have.? Problem with these Chinese controllers is that you never know what's inside so before going any further it might be worth you taking the lid of the control box and take some pictures of what's inside. You could probably re-use some of it. Esp the VFD as they often just remove the front panel and place it on the front of the box. It's easy enough to fit back on and use it.
Don't worry about EMI being a problem because more often than not those having problems have them because of poor wiring practices ie: bad earthing, rather than from the VFD it self.