The amount of
rooting hormone you use depends on the type of cuttings you're doing. If you get a liquid rooting hormone like Rootone, you can adjust the concentration. If it's a powdered hormone, that's a hard thing to adjust.
Hardwood cuttings need more rooting hormone than softwood cuttings. There are instructions on the bottle. Yes you can kill plants with rooting hormone by burning them.
Heck, you can kill plants with too much water or sunshine.
Regards,
Matt