if you want to set up a stock brokerage firm in UK first you need some brokerage experience, to get used to the market and to actually know how to trade and manage yours or your client's portfolio...
As an acronym, I'm not sure. However, a book (of business) is internal slang for the value of all assets under management (AUM) that a person/group handles. Bob: "What's the size of you're book,...