Can someone explain to me the idea of Feed and Circles?

Is feed showing EVERYTHING what is happening in the Circles? Or it can be hand picked by moderators?

Is it possible to arrange that there are for example 20 Cirlcles of different topics with quite active communities inside. But the main moderator of the platform is picking the particular posts to be showcased in the Feed?

Is is it possible to do it that Feed is open to everyone (Freemium) and the Circles are Gated - but (as I mentioned before) some posts from the gated circles are showcased in th Free Feed?