The worst thing is to buy something too cheap that frustrates to the point of turning you off on what could have become a great hobby. The next worst thing is to buy something so expensive and elaborate that it turns you off, or simply confuses with too many choices to figure out on a short diving holiday. Fortunately there is a whole lot in the middle. I would consider getting just the housing, one strobe and no macro-converters, snoots, and what have you. You can add a second strobe on the next trip for better wide-angle and macro converters if that becomes your passion. The Nikon D7200 has been around awhile so you can also look for second hand housings and use the savings to add a focus/video light.
PS: welcome to wetpixel