So, to answer your specific questions:

Effectively none.  There are probably rules around hygiene and so on, to prevent the spread of disease, but beyond that none.

Like I say, bathing in the blood of humans or whatever would certainly raise a lot of eyebrows, but there's no protection for slaves except what they make for themselves.

No; revocation of Rank, exile, death, imprisonment, a fine or even some kind of community service are all more likely punishments.  For an elf, orc or dwarf to be enslaved would be to say that they are like an animal; they'd be killed before that!

Not as written, but it's entirely plausible that such a body could exist (some of the Knights of the White Veil might go for that, for example).  The Wayfarers might have some (limited) sympathy with such an end, although slave rights would cut into their profit margins quite considerably.

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Joe Rooney, the Enemy Of Fun

Insurrection LRP: high fantasy in a dystopian setting.

Bladelands: Raoul Ortez - heretic, medium, bodyguard and scumbag
EOS: staff (probably the best job in LRP!)

Joe R's LARPCard

Also, it depends how that anti-slavery sentiment is expressed, and who it's expressed to.  Just saying "I think humans are people too, despite the fact they demonstrably don't have souls*" will get you looked at funny, but no worse than someone RL who believes animals are equal to humans.  That is, you might get derided and lose some face, but really there's no more to it than that.

On the other hand, it was human rights extremists within Stonehaven who provided the Crimson Blades with the weapon they used to massacre pretty much every orc of note seven years ago.  Expressing sentiments like that to most orcs would be more akin to professing RL support for Islamofascist suicide bombers in modern-day Israel.

And, of course, human slavery is the entire basis of the economy.  If human slaves don't do the work, who will?

So, basically, it'll come down to roleplay and interaction, which is sort of the point.  Anything which promotes conflict where the outcome isn't "rocks fall.  Everyone dies." is probably a good thing.

*: cos you can cut them open and lookee!  No glans ocularis for the soul to live in.

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Joe Rooney, the Enemy Of Fun

Insurrection LRP: high fantasy in a dystopian setting.

Bladelands: Raoul Ortez - heretic, medium, bodyguard and scumbag
EOS: staff (probably the best job in LRP!)

Joe R's LARPCard

Would they be similar to half-african/asians in our own history several decades previous, technically with the same rights but in reality have a seriously hard time in actually getting them? Or is it a case of begruding acceptance (though with a similar level of scorn/disgust and lack of empathy from some parties)?

Having read the setting, and understanding there is definately a sense of uncleanliness about half breeds, just how far you hoping this will go on a general level in comparison to normal humans? Same reaction to a random halfbreed being killed than a random human slave?

Lorien Trust: Tyr Dubh, Dragon, Druid of Arawn

Maelstrom: Kanduras Alberan, Follower of the teacher and explorer extraordinaire!

Bladelands: Shivenko Bhaal, Labarynthine Knight

RL: Mike, the loud one.

There are none.  Half-breeds either learn magical skills/powers or they get killed.  If they don't learn fast enough, they get killed.  Mechanically, this is why all half-breeds are Talented at Magic.

Your other points are pretty close, though - half-breeds are too human to be accepted by their parent High Race, but too dwarf/elf/orc to be accepted by humans.  Even in their specialty, they'll never rise to as much prominence as a dwarf/elf/orc (because they aren't allowed more than Basic Rank).  So while they're not slaves, and do have some rights, they're certainly not as important/accepted as real people (i.e. High Races).

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Joe Rooney, the Enemy Of Fun

Insurrection LRP: high fantasy in a dystopian setting.

Bladelands: Raoul Ortez - heretic, medium, bodyguard and scumbag
EOS: staff (probably the best job in LRP!)

Joe R's LARPCard

Obviously it is potentially a very adult/maure theme. What Caveats if any are you announcing regarding the treatment of slaves and ofc the comfort/roleplay boundary?

I have run into this before hehe