Tipping is not mandatory so it really is up to you how much of the 'recommended' amount you pay... many people don't pay anything at all so don't let others dictate what you should pay. Not saying you shouldn't pay anything (or less than the recommended amount) since the service personnel rely on this money for their wage... but wait til you're on board and decide for yourself.
AND it is not necessary to pay extra for room service, that is also at your discretion.
You will work it out once on board I'm sure!!