Does anyone know if it's possible to create a new document in illustrator that is boundless? And once you have entered all the content you define the size before exporting?
I'd go about this by working with an ignorable artboard, then create an artboard that fits the artwork when the work is done, like this:
Illustrator is effectively boundless anyway, the artboards are more of a convenience for exporting than a limit or boundary.
If you don't want the final artboard to exactly surround everything, after creating it you can resize it by either using the artboard tool to change it visually, or, you can select it with the artboards tool then double-click the artboard tool icon in the tools palette, which gives you a window where you can change the size and shape numerically.