Charles1910 wrote:There are vinyl coated weights that are more practical (Seavenger); is vinyl coated lead good enough for salt and fresh water?
Yes, they are good enough. In fact, these are what I'd recommend for snorkeling, with a basic belt of 2" webbing, a buckle, and maybe a few retainers ("keepers") to keep the weights from sliding around.
Soft weights, shot or "bean bags", are convenient for divers because they fit nicely into BCD pockets, but they oxidize like crazy. Uncoated solid lead weights show very little oxidation but you'll still get trace lead all over your hands. The coated solid weights, if well cared-for, are the safest bet.
Would 3 or 4 5 lb weights evenly spaced provide the best balance - I'm 200 lbs ?
This is difficult to answer because it depends on what protection you're using (wetsuit, drysuit, thickness, etc), physical build, skill level, and how buoyant you want to be. I suspect 20 lbs would get you started in a 7mm wet suit. Perhaps a bit more if the neoprene is new, less if you're a solid mass of muscle.
Suggestion: Instead of a few large weights, buy a mix of smaller ones. For instance, 4x4lbs and 2x2lbs. This will let you add/subtract/move weight easier for better buoyancy control, and it might be more comfortable.
As always, do a buoyancy check in shallow water first to make sure you aren't over-weighted.