I've sailed aboard Symphony and she's a stunning ship! All cabins are large and very elegant, with mohair throws, down pillows and good storage area. Extra out of pocket expenses you may run into are: tips (around $8 per person, per day for waiter, room steward and bus boy); all beverages, including alcohol and coke or seltzer; gambling (this is a total waste and I suggest you bypass it and spend your money ashore); gifts aboard ship. Be sure to dine in the two alternative restaurants -- they're wonderful (both require reservations). Fixed tip for these is $5.
You didn't mention the ports you plan to visit. In some instances, you won't need any shore excursions, especially for cities like Vienna and Florence. The Greek Isles are great for just strolling around. It's best to do a lot of research on the internet and start planning. And, ask your travel agent to get a list of Crystal's shore excursions for this cruise.
A wonderful, wonderful ship. You should have the trip of a lifetime.