If it will be a SMD assembly you also need to check what panel size your assembler is happiest with.
Biggest is not always optimal - it also depends on component quantities to some extent, i.e. if there are lots of parts, the panel-change time is a smaller proportion of overall build time, and there may be yield issues as you get closer to the maximum size of oven,conveyers etc. as well as issues due to warping and placement accuracy over large areas.
IME 400x350mm is a typical maximum size for smaller assembly places, but they tend to spec slightly smaller panels for panels containing lots of small boards.