Will give it a try:
1. Water quenched bulelts will praobly do the job for all with the possible exception of full powered 308 loads. Might do the trick, but generally water quenching gives hardness in the 17-19 range.
(If shooting at low vel., as some 45-70 rifles demand that you do, then the alloy is a bit too hard).
2. Shelf life?...lead stayes lead pretty much forever. As to the hardness of bullets, it depends on the alloy and the hardness level it's heat treated to. Generally, for heat treated bullets, they quickly grow in hardness, then a slow decline over years, eventually stablizing in the 16-19 range. Those that start out in that same range tend to stay there for years and years...who knows for how long...they get shot before too many years.
3. The above should be good for the handguns. Might want some bullets not quenched for the 38specail and 45acp; neither of those two run at high pressures and if the bullet is too hard, are likely to get gas-blow-by leading.
4. yep...going to be 7000gr. per pound. But you have to count in some waste, some oxidation, some "gunk" skinned off, etc.