The wine kits make 6 US gallons. An "ale pail" plastic fermenter is perfect for primary. You stir it up and you have some head space, and it works great. For secondary, when you rack, you have to have some headspace so you can add the finings and stir. So, I've done it a couple of different ways- I've used a 5 gallon carboy and a 1 gallon carboy, and then also I've used a 6 gallon. I've also used two 3 gallon carboys. It doesn't matter, as long as you are able to "split up" the finings correctly.
For example, a 5 gallon carboy is 5 gallons up to the neck, so if you put 5 gallons in it, you still have some headspace. And then I put the rest in the jug. When it was time to bottle, I just racked both carboys into the bottling bucket.
The 6 gallon BB would be perfect for secondary for a wine kit.
Broken Leg Brewery
Giving beer a leg to stand on since 2006