Tipping is big topic which causes no end of bad feeling on cruise forums, but you can choose to either continue to pay the p and o recommended tips, which they will automatically add to your on board account or go to reception and ask to have them removed, or reduced, the best policy is don't tell anyone what you decide to do
but I would always tip the cabin steward if they are helpful, they have always been helpful to me and usually very happy and chatty.
If you have a balcony definitely order room service breakfast, it's lovely to sit outside and eat it or to sit with a glass of something nice in the evening
The biggest thing you should be worrying about is becoming addicted to cruising, I have a friend who didn't fancy a cruise but her partner did, they booked a 7 night cruise leaving last May, since then they have been on three cruises, with two more booked this year and already looking at next year