DB ,To be honest if you're working in 1/72nd you will proably be just as well of with stretched sprue for making the framework etc ...It would probably be about 0.3mm 'ish ....very small , maybe use lead foil or similar for making seats ,milliput for the cushions . There isnt much in the cockpit of a WW I  aircraft mostly the frame tubing / wooden framework depending on what it is ,so maybe various thickness of rod /square from 0.3 up to about 1mm would do .

Chris.