[Given the length of time the series is taking to write, is it possible that there'll be issues if the HBO series goes into production and catches up before he's finished?]

Well, I have a considerable head start.

[Does GRRM have a say in who reads the audio book, and will Roy Dotrice read for the next audiobook?]

I do have a say. Roy Dotrice was my selection. Unfortunately, he was busy doing a play when A FEAST FOR CROWS was recorded. It's our hope to have him back for the next book.