Definitely get another remote, but the steering wheel isn't that necessary.
Motion plus helps, as it makes the remote more accurate and avoids frustrating "glitches/lag" due to how the original remotes are built.
You can also pass on the tennis bat. IMO, all those attachments are only there to show off or to milk people for more money. You won't be looking at your hands while playing. It comes naturally.
Getting the Wii FIT would be the way to go.
That way, you can have fun, excessive, and monitor your progress all at the same time. When you see the lbs start to melt off your wife, you'll be wondering why you didn't get one sooner.
This is all speaking from experience of course.
Results may vary.