Make sure you write your name and destination on a piece of masking type tape and put it on the crate. That way if the airlines paper work comes off it still has your name on it. Are you flying with him? If so ask if you can check his crate in and walk him to the gate with you. Most airlines don't do it but some do. Also when you board the plane ask the pilot or senior flight attendant to comfirm with the baggage handlers that he has been loaded.
I don't know about leaving his collar on with his tags. My advice would be to do it but others might feel differently. I know there is nothing in Cinnamon's crate she could get hung up on.
I would also wear a t-shirt for a while and then put it in his crate so he has your scent for comfort. And if this crate is not his usual crate (or if Marlan doesn't normally use a crate) I would get him use to it several days in advance by putting treats and such in it.
Absolutely ask the pilot and crew if he has been loaded...make a pest of yourself if necessary.
Some people print out a pic of the dog with a short note to the pilot...something along the lines of
Hi, my name is Marlan. I will be flying with you today. Could you please make sure that you can make my flight as comfortable as possible because I'm a little anxious. This is my first time flying.
If you're traveling during extremely high temperatures, you want to ask if the area beneath the plane (where large animals are transported) is temperature-controlled. Some airlines don't have this feature and will not carry pets during the hottest or coldest months of the year in order to protect them.