Why the hell are you farming them? Let the damn things run. It's an island. It's not like they're going anywhere. Animals are only really dirty (disease) when they're farmed. Throw in some large fowl, rabbits, and let the damn things feed themselves. It's not like they're going to be hard to find when you get the munchies.
You people obviously haven't thought this through very well. To start with, you'll need an island at least as large as Gilligan's, just to have a steady supply of fresh water. Farming is dead easy, if you stick to tubers. Salt's not such an issue for them. Several types of seaweed will suffice for the vitamin C requirements.
But weather is gonna be your biggest problem. Finding an uninhabitted island is relatively easy, but all the best ones are already taken. What's left is either in hurricane alley, or too damn cold. The cold ones are gonna take a much higher technology base than you're preparing.