[13lackGu4rd]

1. yes bowl of blood works like any other site searching spell. the thing is that blood sites are very rare, so it's pretty normal you're not finding many sites. but the ones you do find have a large potential to be game breaking(20-60% discount on blood magic mainly), others include free slaves each turn(same as normal gem sites) a few sites that generate other gem types, and even some bad ones like unrest increasing sites(with or without additional effects).

2. generally the higher the blood level the better the blood hunter. sanguine rod counts as +1 blood level IIRC. nonetheless, there's still a random factor, as well as unrest and time. the longer you hunt a specific province the less returns you get over time(it's good to switch from time to time) and the higher the unrest you have in a province the less chance you get slaves(and when you do you generally get less).

3. shift+m is what you're looking for. unfortunately it's only monthly cast, you have no control over which provinces are searched, in some cases like Voice of Tiamat the province selection is bugged, in others it is generally ok, but it's always good to keep an eye on it to make sure it's not searching provinces with 4 sites already or provinces that have been searched already(usually the province your mage is in, or your capital that can't have additional sites).