You should probably check with a lawyer or someone in Tallahassee, just in case, but, as far as I know, when you register the name of your LLC on Sunbiz, it’s already done, but a DBA is a separate thing if you are using a name other than your own without having an LLC (or Inc).
I don’t know if there’s any rule against using your LLC’s name without the actual “LLC” after it.
It’s probably unlikely that you could use a DBA (or LLC) name that’s already registered, even if it’s in a different county, since I believe that’s done at the state level, not just within a county. Then again, since you would want your business to stand out and NOT be mistaken for another, it would probably be a good idea not to use another company’s name, even if it would be allowed in a different county. After all, what would happen if you expand? For that matter, with the new change to the cottage-food law that now allows us to ship our products, it would be better to have as little potential for confusion as possible.
Good luck with your endeavor.