"I've never even used any other brand of housing, so I've no idea whether my Sea & Sea ports would be compatible with the Nauticam, or if I should be looking forward to acquiring all new ports?"
One of the great things about Nauticam is it shares very similar geometry with Sea&Sea. By changing the "rings" on back of ports you can use most if not all on Nauticam. Nauticam also makes an adapter gear for using S&S gearing (and other brands). I switched over from S&S a few years ago for this reason.