That's the fun of it, really. You have complete flexibility. You can make a hop tea to add at the beginning, or dry hop by chucking a handful into the FV, and you can do this at various stages too. And you can do both, even with different varieties each time.
I believe you only get the extra bitterness if the hops are boiled, so that means the hop tea.
If you read the hop descriptions they should tell you want flavours they add depending on when you add them. For example I am planning on using Ella to dry hop some Sundew, because that adds grapefruit flavours, but only if you dry hop with it. I put them in after the vigorous fermentation finishes (after 2-3 days).
I will make a hop tea with Goldings for a English bitter, because I like mine very bitter.
If I wanted something very bitter and with citrus notes, I would hop tea with a high alpha acid hop and then dry hop with Ella.
And so on.
As to the amount, that's up to you also. Between 20g-50g probably. I use "a handful".
