The plants won't root at all in the foam. You would need to surround some planting pots with it. Take a look at my weekend warrior thread and you'll see what i mean. It's not very difficult at all.
As far as securing it to the glass, you have options. You can spray it directly onto the glass, you can lay down a layer of silicone on the glass and spray foam onto it, or you can silicone egg crate to the glass, let it cure and then spray the foam onto the eggcrate. All of them work well, but my preferred method is the latter.
Just take your time, plan ahead and read as many of the build threads on here that you can. Almost any question you have will probably have been.answered at one point or another, if not, feel free to ask away