nmbrook I think you are doing a fantastic job on this. My one comment with regards to modelling would be to avoid silicon adhesives like the plague. If you have a tube of proper siicon keep it away from absolutely anything you wish to glue or paint afterwards. Folk however, often confuse tubes of mastic "silicon" which these days are mostly are acrylic and they are OK but please keep silicon away from everything else you expect to be glued or paint afterwards. It is such a horrid infectious product that the vinegar smelling fumes affect everything else you might want to glue or paint in future and the clean-up isn't worth the hassle in the first place.
...Also to say as someone who has worked on DSV's and converted a pipelayer. I would not be too concerned with matching plans exactly. I'm guessing in an ideal situation for these types of vessel, the design is in principle. I have seen it myself -what leaves the yard is perhaps something different. I can tell you also that some things change within about 10mins of sea trials -what modellers always look for is the builders plans, and whats ends up in service is potentially very different.
For me, you mention ladders in the wrong place -etc, if it were me I would try and represent something so corroded in the first place that although the procedure said the rescue diver should go down there -he wouldn't even consider it in his right mind!
Moonpools on this hullform attract allot of drag I guess. On the Osprey -with "open" moonpools in rough transits -water flooding main deck was occasionally an issue and very wet decks even when on DP. They were very wet areas on some rough transits. There were some very long standing personnel on the vessel who did not understand the concept that the watertight door at the moonpool couldn't be tied-open for "convenience" -eaxactly because this was a huge potential for flooding and any fire to propagate into the accomodation, least-wise form the watertight integrity of the vessel.
Water in the moonpool area at main deck was apparently always an issue. As I mentioned before, we dived in quite bad conditions compared o modern competitirs, I never saw it myself but there was water up the moonpool, flooded dive control, washed down into the old moonpool area. Main deck totally flooded in a deluge. Main deck on this design is not that much above wl, 3m-ish, but when you work in something like 6m sig wave height before any alarms on the bell start sounding etc. In that respect your choice of closing doors on the bottom of the moonpool for transits looks entirely representative.
I would't hit the original makers of the kit too hard. For me I find allot of European kits in different scales are a prepresentative. For example I find railway kits are moulded in some form of pre-coloured plastic -the idea of modifying, painting or even weathering afterwards seems an alien concept. Also, on the other end of the scale, I gave-up on "N" gauge modelling because the quality of the apparanely "acceptable" kits meant I had to file-back detail and replace myself, or other such mis-moulded parts were so badly formed I had to scratch build myself. Throwing away up to 90% of a railway kit is apparently acceptable and perfectly normal. I have always said we do it better from the start in marine modelling.