After making four double batches of marshmallow fondant this morning, I think I finally have the hang of it! The first time my marshmallow boiled over in the microwave. Then I had all the sugar in the bowl to start with and couldn't get it all mixed in. The second time I forgot to add water and I also had all the sugar in the bowl to start with and couldn't get it all to mix in. When I added water, I added too much and that made it very sticky and hard to handle. Finally got it together. I also had to microwave the marshmallows in two batches so it wouldn't spill over again. The last two batches were better. The third one I only started with half the sugar and it kept taking more and more and more sugar. The last one came out fairly easily as I had a pretty good idea how much sugar to add at what points. So I guess I can tell you that practice will improve your technique on making this.. and since it lasts forever practically, you might as well make several batches one after the other and save it.
I colored the last batch light purple/lavender, and am debating coloring all of it that shade for the wedding cake. I made four pink orchids, too. I think I'll make another 5 or so of those. I'll also be using white roses and chocolate shells.