For lettering, I use 'slaters' lettering (for model rail station signs) it makes raised lettering where as the real thing on a ship/boat is most likely recessed (ie. cut into the nameboard, not stuck onto it) but I think they look OK.
For portholes...well it's a bit long to explain here, you could take a look at 'Princess Elizabeth build' in the construction topics and decide wether to attempt it that way (very much like the ones it has already, in fact) - or get the ones from a model shop (much easier/quicker)
What I think I'd do is just keep the ones you have but paint the 'surrounds' black. Looking at the official website picture -
http://www.pskc.freeserve.co.uk/ - the white paint is only a very thin line around the edge between the glass and the hull.... but it's your choice.
I'd try to make the carving using pieces of very thin styrene (0.5 - 0.75mm styrene sheet)...