Delta officially discourages Flight Case decoration, but most folks do have stickers on theirs. I've not ever heard it being an issue, but you are correct to ensure it is tasteful.

Pass travel - the answer is "yes" and you can change your pass rider.

The dinner is something very nice that you will want to bring a date to if she is part of any significant future plans. Most folks wore their interview suits and the women seem to know an excuse to buy a slinky evening gown without much prompting. Senior Management will hand out your Wings (with the star which indicates Captain at most airlines), welcome you on board, take some pictures and give you the opportunity to tell everyone your story on how you came to be with Delta. It is a very nice evening that you will remember.

During your Evac / Emergency Ops training you get to actually inflate the life raft, use the flotation devices and generally have a ball. Guess the joke is what everyone looks like in wet T-Shirts. Got saggy man boobs? I dunno.

Most of the local Hotels run shuttles to the training center. Crash pads are cheaper, but I think a hotel is a little better for getting rest. When you get to Indoc there are bulletin boards and you can get good information from the class ahead of yours that will be all over the training center also.

Welcome Aboard - everyone is glad that you are here!