As a personal brand, you want to create things you enjoy and are passionate about. That is so understandable.
When picking a niche, make sure you choose something that you could talk about every day. But remember, what you talk about is for others to consume. Not for you. If it was for you, there would be no need to post it and make it public.
This actually reminds me of a passage from This is Marketing.
The internet is littered with websites, emails and videos made by amateurs. Amateurs that made something THEY liked. Which is fine. But what a professional does for you is design something other people will like.
My point is; be yourself at all times but think and act like a professional.