Huxy, as far as the watertight doors, at that scale ... I don't know of those are molded on to the model you have or notm but, in general, PE watertight doors tend to look more three-dimensional and realistic. However, since this is your first dive into photoetch, you might want to take it a little at a time. You can always add the watertight doors later if you decide to.
As far as instructions go, again, Gold Medal Model instructions are legendary for being thorough, easy to understand and, in general, a Godsend in figuring out what goes where. There will be absolutely no guesswork involved.