Make sure you curl your lashes before applying any base or color. Once you've applied the base or color, curlling will just take off what you've just applied.

I would suggest one of the plastic ones. However, I also have a nickel alleray and have never had any reaction from any lash curlers that I've used. They don't come in contact with your skin enough to cause a reaction. That is in my case anyway. Your allergy may be much more severe than mine.

I assume the gold-plating is genuine, although probably very thin. On the upper part of the back of my curler, the gold is wearing off to reveal the silver-colored metal underneath, and I've not had it all that long. It doesn't bother me because it doesn't affect the way it performs.
However, for allergies; perhaps the gold is so thin the nickel can still get through to your skin and cause those problems. Or it could be that the other metals in the gold itself(18k gold is only 75% pure gold) might be the culprits. Just a couple of guesses on the subject.

Mine came with two extra pads but I don't think you can buy them alone.

Yes, it comes with two replacement pads for the curling area, but none for the handle area. I just opened up mine today. :)