All TARGET gift cards will be 10% off. And then later you can buy the Disney cards with the gift cards you purchased. I don't think you need a red card, but I'm not sure
I did this last year. The posted limit was $300 for the sale. But I just went multiple times and got $2100 in target cards. I guess the only risk is that they will crack down and not let you buy Disney cards with the target gift cards. It wasn't a problem for me, as of last month. I always just went through the self checkout.