I think NCL is a good choice for your first cruise.
Extra costs for tipping are about 10 $ per day and person. Drinks: beer about 3 $, Cocktail about 5 $, sodas about 2 $, shore excursions: difficult to say, but you can check this on the NCL site:
and then click on the destination you want to go and check out the shore excursions they offer.
They have Freestyle-Cruising, that means, open seating every evening. You have the choice from different restaurants on the ship and the dress code is not as formal as on other lines.
Another good choice is Royal Caribbean, we love the Radiance Class with the Jewel, Brilliance and Radiance.
But check out some cruise-reviews, they can help you a lot.