If I have an 8" two layer cake, and frost it w/ SugarShack's bc frosting, and then have a large, loopy fondant bow on top, will the bc frosting support the weight of the bow? I was thinking I would make a fondant circle on which to place the bow to help distribute the weight. I also want to put some wires with small fondant stars sticking out the bow. Do you think this is too much weight for the bc frosting? I don't want the bow sinking down into the frosting.

Depends on the size if the bow. The black bow in my cake pictures is sitting on top of the cake without support. Yesterday I put my brothers cake topper on top of his wedding cake without supports and it was fine.

I did one last weekend and it was just fine on the buttercream. It didn't sink or anything.

How big were your bows? I'm making mine from the tutorial here on CC, which has 24 loops that started out (while flat) was 1"x6", and then doubled over into a 3" loop. Will that be too heavy? Again, I plan to put it on a gumpaste square base.

If you're worried, you can you do the bow in gumpaste instead of fondant. You can roll gumpaste out paper thin. Fondant can't really be rolled out that thin and can weigh three to ten times more than the thinnest gumpaste bow weighs. I think they look better too...more delicate and thin like a real ribbon.

Also, keep in mind that a 6" strip, doubled over will only give you a 3" if the strip is folded flat over. But a loop has height which pulls some of that length in. Plus you have the bit on each end of the strip that get sealed together to form the loop and sit under the center loop. So if you're planning a bow that is a full 6" across, I'd add an inch to the length of each strip.

The underside of these bows is really no different than a base to sit them on would be. It distributes the weight almost as well. I wouldn't add a base as it just adds more weight without really improving the weight distribution enough to justify that added weight.