I melt scrap lead outdoors on a turkey fryer with a 6 quart cast iron pot on it. It will hold 100 pounds of lead at ¾ full.
Lead boils at 3180 degrees. The vapor/fuming point is generally accepted to be 1200 degrees. Below that there are some fumes, but they cling to the top of the melt. The smoke you generate while fluxing can be kept to a minimum IF you ignite it with a match or lighter.
Flux can be anything containing carbon. Most use plain paraffin, candles, grease, even automotive drain oil. Boolit lube belongs on boolits but it will work for flux, expensive, but it will work. Sawdust chars to produce carbon. Flux does no good just sitting on the surface of the lead, it HAS to be stirred into the melted alloy. Try to get it under the surface of the lead.
As said above, elemental/metallic lead can't be absorbed through the skin. That means bare lead in the form of a boolit or ingot won't get in your body through the skin. However, a lead object that has been oxidized has lead oxide on it. That's the stuff used in lead paint, it's much easier to absorb.
Lead salts like the lead styphonate in primers is readily absorbed. It dissolves easily and goes right into the blood.
I cast in a non-ventilated bedroom that is also my loading room. In summertime. I DO have a window open, with a fan behind me to keep ME cool, not for smoke/fume control. I just had my 3 month blood panel done at the VA 6-28. I had them check my lead level, it was 9.0. I was curious because I've been doing a lot more casting in the last year. Pretty good for no ventilation! I've been casting since 1972, don't plan on stopping, until my Lord brings me home!