I saw Billy Porter in New York and whilst he is very good, I don't think its the be all and end all to have him over in London. I recently caught the tour of Kinky Boots in San Diego and the Lola was excellent. Would be great to find an unknown to play the role.
Jon Robyns would be great casting for Charlie but I think there are any number of people who could play the part really well.
The interesting casting for me will be Lauren, she gets a hysterical song in act one and you need a great comedic actress to play it. Nobody springs to mind immediately though.
Personally, I think that Edd Post would be a perfect Charlie! I'd also love to see Nicola Brazil as Lauren - she's an incredible actress and I think she'd be great in the role. Ideally I'd love for Billy Porter to come over with the show, but if he doesn't I think that Tommie Earl Jenkins/Tee Jaye would make a wonderful Lola.