Yes you can stack them. You need to have a proper stacking kit, though, and not consider just putting the dryer on top of the washing machine underneath. I know, 'duh!', but some people have done that! It would work very well then, except perhaps you may have a problem with emptying the drawer of water after each load (on a condenser dryer) because you might find it to be quite high (and awkward) to access.
A more expensive brand of condenser dryer means that you'd probably get excellent results siting it anywhere in the house. A vented one would be loads cheaper but needs the hose to be out through a window or vented through the wall.
A washer/dryer as so many have said - I'd say Nooooooo !
Biggest problem is that you can't use the washer and dryer at the same time, so if you have lots to do this wastes time. The dryer will not continued and dry a maximum load without a lengthy drying time, and then will likely be very creased since the washing hasn't been sorted and shaken out beforehand. It's recommended to remove quite a lot of the wet washing and dry it in smaller amounts so that it tumbles freely, less creasing and more even drying. I wouldn't want to trust any dryer to be running in my home if I wasn't there - but that's a personal choice. If you're going to buy a condenser dryer, get the best you can afford and - if it were me - I'd rather compromise on space than be driven mad by laundry problems, but your idea of stacking might be just the solution you need. Hope you'll be thrilled when your new kitchen is completed.
Lack of public toilets in towns.