The 'brown' stuff is likely diatoms, this is very normal in an immature tank and will eventually go away as the tank balances in. In the meantime, yes, you can clean that stuff off.
I don't know what the 'fluffy' stuff you are referring to is. A picture would help.
This is one of the ornaments. You can see the dark stuff, and a little of the white "fluffy" stuff. This isn't as much as last time. I sucked up what looked like one of those little, round spider pouches off this guy last time.
That's about as good as I can get of the white stuff this time.
What about the dark greenish brown stuff? You can see it, too. It's all over Nemo, the castle, the volcano, you can now even see it growing on the black rocks at the bottom.
What does it mean if the glofish are bumping into the glass a lot after feeding them? They seem to swim pretty much normally, and then after feeding them, they all bump into the glass at the front of the tank quite a bit.