Andrew,
Sounds like you've done your research (Reading MYCNCUK with a pack of HobNobs and a large pot of tea?), I'm looking forward to reading the build log. Jazz will love you for not having actually bought any bits before asking for advice
My only suggestion would be to make the bed a bit longer if you have the room for it. My own machine can cut a little over 600 x 900. It doesn't affect the gantry in any way and I've never had a project that needs all that area at once yet, but a bit of extra length has proved necessary on occasions. My woodwork projects seem to regularly require parts that are narrow but a bit longer than a 600mm square machine could cut in one. Mostly accessories for my wife's weaving hobby.