Hose diameters vary from model to model; the manufacturer matches the size to power and capacity. You will have some choice on hose length. A longer hose is more convenient, but length reduces suction.
Where the hose attaches to the tank, look for a screw-on or locking connection so it doesn't pull loose when you tug on the vacuum.
Since wood dust is a carcinogen, choose a vac that comes with a HEPA filter, which can trap particles smaller than 1 micron. (Or buy one to fit your vacuum for $25 to $70.) Look for models with a filter bag inside the tank, so you don't end up with a mushroom cloud of dust when you empty the tank.
Some models work as a pump, which lets you hook up a garden hose to clear out a flood.
Watch out for a short power cord, which forces you to drag around your own heavy-duty extension cord. Look for a built-in cord reel for long cords.
Most vacs include a floor sweep, crevice tool, car upholstery tool, and a wide water blade. Make sure the tools can be stored on-board so you have what you need where you need it.