Just been on the Jade Med cruise two weeks 13th June. I believe no ship will allow irons in cabins due to a fire risk. Regarding clothes, everything is so casual you will not need as many changes as other ships. There is no dress code in the evenings which spoils the whole evening atmosphere of cruising. Men did not wear suits/tuxedos or women evening dresses. I was on the Jewel two years ago and there were two formal nights each week and everyone dressed accordingly i.e. evening dresss and tuxedos and the passengers were very happy to do so, this being an important part of cruising.
Informal nights were adhered to, gentlemen wearing suits and casual nights shirts and trousers and certianly shorts were not permitted in the public areas after 6 p.m. The food was excellent though in the Garden Cafe there were no trays so one had to go backwards and forwards for food. On the Jewel there were trays and the staff were always offering to carry them to the tables. So do not worry about your wearing apparel - unfortunately no-one will notice as things are so casually disappointing.
No, most ships regard irons as a safety hazard, but you can take your own but you will not have a table to use it with so best not to. The ship does a have laundry special once per cruise when they do cheaper deals, ask about that, your attendant should have an idea otherwise the facility is not cheap.