You can give a generic brand name as long as the real owner of that brand name doesn’t raise an objection. Unless you do your home work properly, chances are that the brand name you considered as “generic” is a ACTUALLY someone else’s intellectual property with registered trademark.

As soon as the real owner raises the objection, you’ll have to remove the name and all the hard work done for setting up your shop will be destroyed because if you don’t stop using their brand name, they’ll legally sue you for stealing their intellectual property. Consequences could be very serious including hefty fines, jail term and loss of time and money you wasted in nurturing a “generic brand name”. So, please be sure with what you want to do…

Your other question about the Brand Registry: you can apply for the brand registry ONLY if you’ve a registered trademark for that brand.

Your third question: yes, you can sell under any name without having the need to register it. Registration protects your brand name from possible thefts and misuse of your creatives, contents and other intellectual property associated with it. Tomorrow, if your generic brand grows so much that a person with time and money registers it as his own, you’ll be left with a generic brand name while this person reaps the fruit of your hard work.