Wearing a uniform may be a good idea, I did it one time years ago.
It is optional and may help you get through security in Europe if you have liquids, etc.
On the other hand you may want to keep a regular street shirt handy as once you get underway you have the option of remaining incognito. You do not get included on the General Declaration as a crew member and in the other end are subject to the same entry procedures as a regular passenger. At this point a uniform has long since lost it's usefulness and you can avoid the awkward questions and the gawking...