Full disclosure: I returned to building scale model kits in mid-2019 after a break of more than 60 years. Back then, I would complete a model, including decals, while the paint was still drying! Ergo, I am still an amateur! However...
If I were you, I'd forget kit-bashing this particular model to add the lower part of the hull as well as the rudder and screw. Waterline ship models simply display ships as most people see them, in the water with nothing visible below the water. Working for realism above the waterline is far more important, and will require some tasks which require a steep learning curve, take a lot of time, and inevitably include some mistakes, some of which can be fatal, not to you but to the model, although some of my mistakes made me feel suicidal!
Three of the four models I have completed are based on actual, specific aircraft, two of which I flew in and one of which I learned a great deal about while researching the death of a Canadian airman in the Second World War. The fourth model is of the U.S. Navy hospital ship Repose, on which I was a surgical patient after being wounded in South Vietnam. Repose kits exist, but they’re rare and represent Repose as it was during the Korean War, not the Vietnam War, so I had to start with a model of another Haven-class hospital ship, S.S. Hope.
Each of those models required DIY decals, addition of various antennas, roundels, changes of paint schemes, addition of camouflage, hull numbers, registration numbers, and even static wicks. The helicopter that came with the hospital ship, supposedly representing a Sikorsky UH-34 Seahorse, was far too small for the scale and didn’t even look like a Seahorse, so I scratch-built a larger, more-accurate one. I’ve used printer paper, sprue, wine bottle stoppers, brass rods, and carpet thread to add details to my models.
While 100 percent accuracy is a worthy goal, it’s not necessary to build an attractive, realistic, and very satisfying model.
Bob