As a long time fan of buck and ball loads here are some of my observations.
1. The load will recoil slightly more than a standard round ball load if you use the same powder charge as you do with your roundball load.
2. I have never felt that saftey was any more of a concern with buck and ball than it is with any other type of projectile. As long as amounts (powder and shot) are kept within reason there shouldn't be much problem. Most would agree you DON'T need 200 grains of powder and a round ball along with 30 pieces of buckshot. Keep the powder chare within you usual amounts and it shouldn't be a problem.
3. As to what size buck and how many to use it depends on the gun. I have found that in my 20 bore, 4 #4 buck will sit nicely on top of a round ball, additionally 3 #0 buck will do the same. so load in flat layers and you shouldn't have any problems.
4. As to the ball over or under the buckshot I would suggest trying both, some guns do better one way or the other.
5. Patches/wads. I usually patch the ball if it is a size ball I would usually patch i.e. a .590 ball gets patched in my smoothbores whereas a .600 does not. load accordingly but make sure it isn't going to creep up the bore (put a wad over the shot and ball if it will move.
6. Effectiveness is only going to come from experimentation and practice. Try the load out. Generally buck and ball is a short range load (under 30 yards). With one of my guns it works okay as a long range load (the ball carries true out to around 70 yards with the buck being way to scattered beyond 30 yards).
All that being said the load I use in my guns (matchlock, early flintlock, and mid 18th century fowler, all 20 bore) is 70 grains of powder underneth a wad (leaves, tow, paper, etc.) with a round ball (.590, .600, .610 depending on the gun) followed by 4-8 #4 buckshot overtop all capped off with another wad (tow, leaves, paper, etc.). The load is good for me out to 30 yards in all cases with the full sperad being about 12-15 inches at that distance with the ball more or less in the middle of the pattern.
Try a couple differnt loads and be careful, the above is just what I have found to work not nessacrily what I would recommend for all guns. I have had great luck with the loads taking deer, coyotes, bear and wild hogs as well as many a steel silloute.