I'd think about adding some curves. Allows more internal capacity and gives you room to make some fine embellishments as the other liners have to mark their "luxury" aesthetic. Don't be afraid to stretch it out, either, the bridge portion and engine sections of existing liners are quite small in comparison to the rest of the ships. The Elbe does a good job of taking the Rheinland look and making it larger, less blocky, and more attractive to look at (since let's face it, that's why we fly liners in the first place).
