you mention "just a door" for the washing machine.
It's quite usual to have a washing machine standing on the floor (not on the bottom of a cabinet) and this will be a stronger and more rigid support, so I recommend it.
Appliances are usually 600mm wide, you you would need a gap, and a door, a bit wider than that. Or a competent woodworker can add a bit of matching trim to a 600 door to make it cover, say, a 650mm gap. It can have a bit of dummy or removable plinth.
if the space for the washer was exactly 600mm wide, the washer would slide in, but with no room for hinges, and a 600mm door would not have anything to butt against at the side (a 600mm unit, which the door fits, has 18mm walls each side, so the internal width is about 564mm, with the hinges projecting a bit inside). If you measure the door, and the internal width, of a cabinet you will see what I mean.
Or you could have a wider space, such as an 800 or 1000, with double doors, and room inside for your washing powder, fabsoft, etc.
Some manufacturers have a wide range of odd-sized doors to fit such eventualities. Or they might charge extra to make one to fit. Find this out and discuss with your installer before you order. Mass-market vendors may not be accommodating.
Blum now make hinges that are click-on and can be removed in seconds for easy maintenance access with no tool except your thumb.
An integrated washer can have a dummy panel fixed to the front, but I'm not keen on them, they are poor value and it will be hell when you want to take it out and fit a new, different, one.