When you understand how branding works in the commercial world it's very clear on the answer. You advertise based on the name you're going to use when you release your games, and when you communicate you're posting as (name) at (studio name), but should bring attention to your company name. People in the industry will recognize you over time by your personal name anyways if that's important to you as you get to know and meet other developers and fans of your games.

As a business person I don't brand myself as an individual, especially considering liability issues. It is all done under limited business entities which have names registered under them which are the brands.

No, Rutin is just a name I use only on GameDev. I haven't chosen to promote any of my businesses on GameDev at this time. I'm active on other forums too but I use different names.

depends on how you interact with these online communities. are you promoting your games? are you there to learn? to share your development experience?

if you're promoting, then it might help to use the brand name. for instance, if you're doing so in a facebook group, you should probably post there as your company/brand page rather than your personal account, might help with getting followers/likes. if you think you're going to use an online community for anything else than professional work, it might be better to stick to a nickname. you may never know when you get into an argument with someone, throw some heavy words and well, tarnish your brand name ?