Welcome to the forum :)
I don’t mine anymore, but I think you don’t need a SDK to mine with nsgminer.
Check out the mining section here. There may be more specific information available there.
the .dmg file is the one you need to install.
the .dmg.asc file cointains the signature, so users can check that the file downloaded was created by one of the feathercoin team members.
I don’t use a mac, so unfortunately I can’t explain which software you need to verify the signature or how to install the .dmg file.
In any case you can install the dmg file without checking the signature. That’s your risk
Hi! What miners and software exactly you use? I want to start mining but such issues look a bit frightening. Now I choose between traditional mining and cloud because the latter provides more user-friendly and easy-to-start options with discounts (like this http://ccgminingcode.com/). So, would be cool to know your equipment, profits and possible problems to compare these approaches. Waiting for your reply.