Hello,
A - I'm sorry, I can only reply to questions regarding HikaSerial (and some about HikaShop), I'm not Acymailing expert.
As I told you previously :
There is no user assignation with HikaShop coupons.
I'm afraid that I can't change the fact that this feature does not exist in HikaShop.
C - The coupon have different kind of restriction (product, category, order value, nb of product, zone, acl..) but you can not use them if you don't need them.
By using the quota on the coupon, you can be sure at least, that the discount will work only one time. It will be a unique coupon.
Regards,