I'll take a whack at this, not a doctor and actually quite new to ML hobby.
1) I have incredibly sensitive hearing, and I wear your standard ear gummies with headphones on over them. 5.56 rifles make my ears ring still. I fire my blunderbuss and have fired a long rifle with only ear gummies or headphones, and it doesn't seem to have any ringing effect.
2) Smoke from a black powder rifle would probably be the same as smoke ingested from any fire, and probably 1:1 from inhaling smoke from the 4th of july when all those fireworks are going off. Its not good for you, don't be huffing it out of the air like a weirdo. That being said it typically isn't blowing into my face and I don't get a lot of it in my lungs. Basically treat it as you would any other smoke.
3) Eye protection is highly recommended because flint does break off tiny pieces. Some locks eat up flints quickly and spray shards. Others barely anything. The fireball flash and everything else is fine and won't hurt your eyes. The only thing is the bits of rock that can fly off. If someone is standing to your right they will probably feel something. I've never been hit in the face with rocks, but I've only been doing this for a few months and I've heard some people feel grit hit their forehead or whatever. Its mainly a non issue but still highly recommend it. Smoke in eyes would be non issue, your eyes are good at catching and filtering that stuff out into tears that you wipe or blink away.
4) Recoil is absolutely nothing compared to equivalent arms. I fire a .69 round ball and is significantly less impactful than a 8mm mauser rifle I fire often. The 8mm can actually bruise me. I let me 95lb sister in law fire the blunderbuss even with horrible firing posture because I knew it wouldn't be enough to hurt her. Unlike modern guns that are snapping and punching your shoulder while launching projectiles, the recoil is more like hanging onto a tube as a combustion happens and pushes your ball out the other end, and its still recoil but it feels more gradual (Within a fraction of a second).
PS EDIT: Make sure to wash your hands after handling all the material like lead balls and powder. Try your best not to touch your mouth and eyes after touching lead. Don't be one of those guys that put the lead ball in your mouth and you should be fine lol.
I'm pretty sensitive of my hearing, and I'm scared of toxic stuff, but most of the stuff in Black powder is pretty safe. Lead is the biggest thing and I just make sure to wash your hands before doing anything else.