No, you won't lose any items, and your ui will remain the same. The only thing you can lose is gil if it exceeds the transfer limit. Currently it's 1mil on your person and 100k on each retainer, so if your retainer is holding more then 100k you should invest in some items that you will be able to sell on your new server to make that gil back. Heres a link you'll find useful.

http://na.finalfantasyxiv.com/lodest...nsfer_service/