It depends on the project, if you intend to openly write about your belief and exposing the enemy you should rethink your course of actions.
If you are trying to simple black metal songs there's no harm. Always be mindful of what and who is around you, unless you don't intentionally made neon signs showing your location and how many times you meditate per day you should be fine.
Always keep it for yourself, unless you are dead sure of the opposite.
"You never know those who don't know what could do". -Father Satan.
Yes, the main thing is not to make public statements about your faith, because in such cases the enemy may guess that you are not an ordinary black metal player.
You should definitely start your Black Metal project, I wish you success and reaching heights in your new endeavors!
For now, you should. Help us with the ritual schedules and other projects so the sooner SS can be known to the whole world instead of hiding our beliefs for our safety.
I would recommend that the lyrics and songs of your black metal band talk about pagan mythology: runes, gods, legendary heroes, pagan philosophy and say that you are a pagan, but never say in public that you are a SS.
I do not really think you will have much issue if you are only going to be online, maybe from jew trolls but that's it. However I would highly suggest keeping to your own if this is something you plan to do in real life, having shows.. meetups and such.