Series 7 Arne Jacobsen chairs, Which Paint?  

Paint
Polyurethane paint is what the factory uses, so yeah, that should be ok. The difference between their opaque and translucent painted finishes is just the number of paint layers.
I wouldn't care about the labels, but some people do, so it wouldn't be a terrible idea to mask them before painting. You could also try to remove them before sanding and painting, then re-apply them after, but that might not be easy; I just checked the labels on my chairs, and they're secured pretty firmly to the wood. You'll probably need chemical assistance to get them off; in the UK, I'd look for Sticky Stuff Remover (URL below).
Put a drop or two on the label and wait for it to soak through to the adhesive; the label should then lift off without tearing. The label may end up looking oil-stained, though, and/or the ink may run, so test it on one before doing all your chairs. The product should be compatible with the paint already on your chairs, but it doesn't really matter, since you're going to sand and repaint anyway.
Just be sure to wash the area thoroughly after the label's off; the Sticky Stuff Remover is made from petroleum distillates, so it may interfere with sanding (and the new paint probably won't adhere to it very well, either).
Good luck...
http://desolvit.co.uk/pages/sticky_stuff_remover_liquid.htm

label removal
WD-40 will do the same job as the other product previously mentioned for label removal and for same effect without the oil residue MEK (methyl-ethyl-ketone) is the product of choice.