I've nearly completed a card 1/400 U.S. Attack Transporter and that's a tiddler at 16"
Some pointers that you might find useful......
Use a steel rule and a very sharp blade. I use a 10A Swann Morton. The 11A is too long and difficult to control.
You will have to build such a big ship on a jig of some sort. I used a thick piece of plywood and built on that. You have to do this to keep everything square and true.
Be deadly accurate with your cuts - wander off just a bit and it's goodnight.
Make sure you get the initial frames and bulkheads and box sections spot on. Get these slightly out and the actual ship's 'skin' won't fit.
I hope the above is of some use to you.
Best of luck. Just take your time and make sure no one is about when you make the model. Then you can curse as loud as you like....I do!