Sometimes I start with flavour: imagining the badass fantasy in my head (or finding art that inspires me) then picking feats that fulfill that idea most closely.
More often though, I'll be reading through the feats and find a really cool feat chain or capstone and create a flavour that would allow me to utilize those feats. I then end up picking the filler feats to match the existing flavour like in the first example.
So...both? Yeah. Both
I'd love to help out. Reading about the mythos of other cultures has always been super interesting to me and this'll give me an excuse to do it even more lol