Hello,
You have to do it in the front-end where HikaMarket can provide you an interface fully compatible with the multi-vendor feature.
The HikaShop characteristics edition in the backend don't have for the moment the required elements to allow HIkaMarket adding its fields.
It's possible to open a feature request so we can implement it in HIkaMarket.
But if you want to do it with the current version, the front-end will be the solution.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.