You might go poke around the office supply store to see if they have acetate sheets for overhead projectors.
These can be handy as glazing for portholes, as strips of the acetate can be set on the inised of the hull en masse. Those can also be hit with Tamiya Clear Smoke or Blue or the like, as not all staterooms will have the lights on.
Acetate is also good for the insides of long deck houses on the upper decks, too.
The xmas lights are appealing as they are inexpensive and long lasting. Only two issues with those, though.
One is the light is a very blue-white, rather than a warm sort of white (which would be more prototypical with the Edison lamps that would have been on Titanic.
Second problem is that they are line voltage, which means you have to be extra-careful with joints, splices and the like. Bad joints at 110VAC equal heat, and plastic and heat do not get along well.
Probably worth browsing the model RR lighting stuff, and the Sci-Fi lightinh stuff to see the sool suff that is available.
Big liner hull makes a tepting place for battery packs. But, that means having to figureout how to rig one of the superstructures to come loose so you can get in side. Also, unattended batteries will leak. This is never a nice cleanup.
This is where I linke using one of the screws that passes through the finial into the base as a positive, and another as the negative. That means you can put a battery box, as replaceable battery box, in the base. Or, you just get a connector for a 12VDC, 6VDC, or 3VDC "wall wart" transformer to plug into.
Sadly, there is not a Radio Shack on every corner chock full of cool bits for this. But, there are plenty of places like Fry's and the Ilk who can supply all kinds of cool things. Like motion sensors--which are really cool for only working when someone is around to see the effect (trust me, the cat will lose interest).