Yeah the wheel is just another axis to the computer and game like any joystick. I like the G-25 as it can turn 1,5 (I think, dont have it in front of me) times in each direction whereas most other wheels can only go 90 or 100 degrees each way. Force feedback can be set to keep the wheel steady, so when you let go, it stays at that angle. Perfect for a ships wheel. It is also a very expensive piece of kit and unless one is really into car racing it's probably not interesting.
My throttle quadrant comes from the "SAITEK Pro Flight Yoke System" set, together with the push/pull yoke, and I picked it up on german ebay from Computersource.de (was living there at the time). One negative point is that the throttle quadrant has to be attached to the rather large yoke-module which again plugs into the PC, so youll need somewhere to store the yoke out of the way but not too far (for the wire). Yoke is not practical for steering a ship, it will only turn a "few" degrees like the yoke in a Cessna.
You can also get the "Saitek Pro Flight Throttle Quadrant", which is only the TQ, at around 50 euros or lower. That one is USB and plugs directly into your PC. For shipsim that one should be "perfect" for throttle. Also some buttons on it for various functions. One downer is that there is no "middle mark" to let you know when youre at "idle". It might take some time to get used to where the 50% mark is on the yoke. I used a tape strip with a bright color to mark it off so it was easier to see at a glance. It would still be nicer if there was a physical notch the stick would fall into if it was to be used primarily for boats.