Hello, 1st time cruiser, and welcome to CruiseCrazies! Congrats on your 1st cruise. If you think that your addicted now, just wait till your cruise is over.
I'll try to answer most of your questions. First, I have never been on the Carnival Inspiration so I can't answer anything about that ship. I'm sure that there are more than one on the board that has been on that ship.
As for weight, my wife and I have never gained more than 2 pounds on any cruise. Just keep active and there should not be too much of a problem. Carnival will charge you a flat fee for the tipping which will go on your final bill. You can adjust how much they take if you don't like the service you got. At the end of the cruise, you may also give extra if you really liked the service. Tips are added directly to the bar bill as you sign for it. BTW, use any credit card you like. They take most cards, and it doesn't have to be a Carnival card. As for dress codes, the only thing that you don't see in the dining room at dinner is shorts, but maybe I'll let one of the young ladies on the board give you dress advice.
Enjoy the anticipation. It is all part of the cruise experience. When you get back, and book your next cruise, the anticipation doesn't get any less. :grin:
Howard