I don’t know that my opinions are “expert”, but I’ll try to answer a few anyway .
I think the biggest problem you are having is that you are not firing hot enough or holding long enough. The more heatwork the glass experiences, the smoother and more rounded the edges will be. So…
1 – Yes Some people cut the top piece slightly larger to ensure that it folds over the edges. However, if you think about how the glass will flow, it’s not necessarily required. The glass touching the shelf will flow less than the glass on top. With two layers of glass, this difference in flow is minimal. With more (undammed) layers, it will be more pronounced.
2 & 3 Again, yes . You can refire, or, you can coldwork (grind or sand and then polish). It depends upon the look you are going for. If you want rounded edges, I would simply refire. Because these are small pieces, you are likely safe with your original firing schedule (though you don’t say what that is). If you want squared off edges, you can coldwork to a high polish, or coldwork to a rough finish and then fire polish in the kiln. (good book for beginners – Cold working without Machines http://coldworkingglass.com/).
4 (and 5) A basic tenet of fused glass is that “glass wants to be two layers thick”. So… if you stack two layers, the piece will be roughly the same size when it comes out of the kiln. If you fire one layer, the glass will still try to round up to be two layers thick. What you’ll end up with is the sides pulling in (this is affectionately referred to as “dog-boning”). Conversely, anything stacked thicker than two layers will spread if subjected to sufficient heat work. You can allow the glass to flow, or you can use means to dam the glass so that it doesn’t flow. This layered look you refer to is typically achieved by stacking glass, damming, and then firing. You can also do it two layers at a time, but once you stack additional layers on two, you’ll likely want to dam it to control the flow. For pieces like this, you can make pattern bar “slabs” (I’ve posted one of my pattern bar projects here: http://jestersbaubles.blogspot.com/2013/02/2013-magless-exchange-stained-glass-look.html) You then cut up these slabs into the size of cab you want.
I hope this helps to get you started. The best teacher is experience. You might want to start with less expensive glass (dichro is expensive!), and practice with that.
have fun, Dana
Jester’s Baubles Fused Glass Designs