DCL is not that uptight and fellow cruisers can understand that first day can be a bit hectic. Esp. when having early dining. If something does happen, c'est la vie and just join the diningroom as you are. Anything that you can't be without; keep it with you!!!!!!!!!!! While odds are very very small, with those things you don't want to run any risks. You could perhaps have a change of clothes in your carry on when for instance flying in transatlantic on that same day (could so understand wanting to freshen up and not wearing those travelclothes to dinner), but I wouldn't be that worried about perfect attire for that first night. And that's coming from somebody that very much values dresscode and sticking to them.
Had a verandah on our previous cruise, but there have been many topics on this on the main DCL board. Very common tip; have a small flashlight or something nearby in case one of you needs to use the bathroom during the night and not wanting to light up the entire room. It is dark!
If you are the type of person that wakes better with natural light; turn your tv onto the channel that shows you the cam on the bridge. It'll broadcast the sunrise and lighten up the room naturally.
As it's dark; you want some way to tell time when waking up. Consider a small light up travelalarm or flashy light to use to be able to actually see your watch.
The dark is lovely for napping. Oh you, totally relax on your vacation.

Just be aware of the risk and do not fall into the trap of drifting of in the early afternoon to find yourself not waking up until 10 pm or so, having missed all of the fun and now being wide awake at night. Oops. I've even seen some people do this on our cruise with verandah staterooms.

Set an alarm "just in case" if you are the type that might drift off so you don't nap too long or miss that much anticipated activity.