If you don't have the - and + symbol, it means that you changed the option "Display the quantity field on the product page" of the Display tab of the configuration which controls that.
If you can't buy the product, you might want to check the variants of the product if you have some for the same options as the main product.
Also, we solved a problem yesterday with that so you might want to download&install again HikaShop. That might help solve the problem easily.
For HIKA_USER_NAME, that's because you're missing the translation key in your language file. You can add it in the Languages tab of the configuration.