Daisy May Cooper sells it for me. Never heard of Mawaan either but there is usually an unknown in most line ups. Casting no different to on Dave really, though TBF they always punched above their weight with the casting.
Richard Herring has been hinting for ages that he wants to be on it, especially when he had Alex Horne as a guest on his podcast. He's an Avalon name so was bound to be on it eventually. He recently tweeted that he's been 'doing some telly' so it was fairly obvious what.
Johnny Vegas is a great choice, I can imagine him and Greg Davies working well together. As is Katherine Parkinson. I'm not familiar with the other two