Hi Toby
Welcome to the forum, hope you didn't spend a lot of money on your plans.
Sad truth is wooden routers are not upto it, especially @ the size you are thinking of. If you had browsed the forum you would have found that plenty of people have asked the question and all received the same answer.
I don't know what sort of precision or repeatability you are looking for but to be honest you are going to have to go with steel frame @ this sort of size machine.
Regards
Mike