When you're harvesting the blood iron of your enemies you don't have time for ethics. A controlled study managed 4 weeks within ethical boundaries, maybe we can cut that in half unethically. So 14 days, 3000 . 14 = 115 years. So when you torture two people, you could manage to do 58 years. Better start early!

You're off on blood production. "Safe" would be once every six to eight weeks for a pint. Plasma can be taken a lot more often. The red blood cells take a while to replenish.

But let's get real. You're not concerned about your enemy feeling well. Force them to take iron supplements and take a pint every other week. They'll likely stay alive that way. Fuck em, right?

But remember they are your enemy so you could drain a bit more blood more often to shave a few years off maybe