Planning is good! However, there are extremes at both ends of the planning scale.
There is nothing wrong with having the basic information as long as you have realistic expecations of what to expect from the cruise. I strongly believe that overplanning is as bad as under planning, especially once you board the ship.
I often feel sorry for a new cruiser who comes to the boards and reads "one" negative post about a ship and thinks they made the mistake of a lifetime or reads something positive about another ship and suddenly has buyer's remorse. Sometimes it's nice to let the experience happen. Just about any relatively new ship can be a wonderful experience for a first time cruiser.
I can spout the tonnage, number of decks, basic cabin layouts, which specialty restaurants are available on what lines and ships right off the top of my head and sometimes I wish I couldn't. It takes some of the "freshness" out of the experience. There have been times I wished I didn't know as much as I did but there are many times that I'm glad I did.
So: My recommendation is to get the basic information out of the way: Booking number, online check in, basic packing info, what the dining experience is like and an idea of what you want to do at each port and then just let the experience happen.
Remember: It's a vacation and not a military operation.