You can also primary in a bucket, if you have one. Then you don't have to worry about the primary being too small. The 6 1/2 gallon is going to be a very tight fit, although you don't get the huge krausen like you get with beer.
And, like Jsin said, you can used sanitized glass marbles in your secondary so you don't have too much headspace, or to top it off with a white wine. I wouldn't top off with water, because then you're watering down your wine!
You don't need more equipment, and it IS easier than beer. If you can brew beer, wine is a breeze!