@Sep Hello William, and welcome to the forum! This page has the dimension and recommended table sizes for the different LongMill MK2’s. You will find a lot of useful information in the Resources pages. It’s a good place to learn about your machine while you wait for it to arrive.
The machine you ordered is basically gonna need just over 5’ wide and 4’ deep just to fit the machine. They say that 6.5’x4’ is a good size but If I had the room I would consider going 8’x4’ because you need a place to put the control box, your monitor and keyboard.
Since you are in the process of designing your table I would feel amiss if I didn’t mention the possibility of incorporating a way to mount boards vertically. I don’t know what type of work you plan on doing but if making dovetails and other type of joinery interests you it can be done with a vertical setup. You can see my vertical setup in this thread and another in this thread.
EDIT: You also might find this thread interesting as it has a lot of tables in it. It might give you some ideas.