Yes, they can increase fees twice a year if they wish. They always want to.

How much is anyone's guess. Usually it is a small amount 50 or 60. The year I applied for FLR the fee went from 500 US dollars to 1,000 with about a month's warning, so bigger raises can happen, but they are unusual.
You can either mail it in, which is cheaper, but it takes longer. A lot longer.
You need documents spread evenly over the two years. I just kept all my mail in a folder and then sorted it out the month before. You need to keep things, but no point in getting it all together a year early.