It may take a couple of days for fondant roses to dry all the way through. You can store the finished roses in a box rather than an airtight container (I use the cardboard tray that bottled water comes in, lined with waxed paper dusted with cornstarch, and then tape waxed paper over the box like a lid) and then they can finish drying at their own speed. They will keep for months.
The only time I ever had a problem with fondant and grease from buttercream was the first time I made fondant, and it was a weird fondant that didn't have any fat or gelatin in it (didn't work very well by the way). All the fondant I've made since then has been marshmallow fondant and it works fine on buttercream. I've even put dried fondant flowers on a buttercream swirl on a cupcake and left them for a couple of days, and the fondant doesn't absorb any of the grease or wilt.
To make your fairy, you can use toothpicks and straws or coffee stirs or hollow lollipop sticks as modeling tools. I know one lady who uses her metal knitting needles as a fondant tool. You can make the hair with your garlic press too. To make glue to stick the fondant pieces together, dissolve a small piece of fondant in water, or mix some meringue powder and glue. If you have a butterfly cookie cutter, I bet you could use it to make wings.
Thanks so much for all of the great information. The idea about the garlic press is fabulous! I never would have thought of that. Do you think that I should put a stick down the center of the fairy for support, or just do it in steps until each step is semi-firm? Sorry about hammering you with all the questions, but i don't want to mess up and be scrambling last minute with a cake. That is part of the reason I wanted fondant pieces is so i could make ahead of time and just assemble later. Thanks again.