our LG pair is about 4' 6" wide & 31" deep + 4" for vent + door opening, ect. Washer plumbing could be in a recessed box in an (inside) wall. Most dryers can be side vented (if you have room) Dryer vent could go through back wall, floor or side vented (or through side wall), ect. We have them on pedetals on the concrete basement floor.

Seems normal for a US front loader. Because home in the US are usually a wooden construction, vibration can easily become a problem. That's why manufacturers have invented all sorts of anti-vibration technologies and added a soft suspension that's cancels out most of the vibration. See how this models even wobbles with an empty tub at 2:30 -> http://youtu.be/DHaAqiCGpIk?t=2m Alex

Pros: More compact, takes up less space. Can put in 1/2 load and just let it go until it's done. Cons: If you try to do a full load, you either have a very, very long dry time or you have to pull half the load and dry separately. Capacities usually are not very big so only good for a single or couple probably. With the long times involved, since you have to wash then dry since you can't be washing a load while another is drying, you probably would have to do loads more often. Not the most conducive to a once a week laundry day, especially if it's a work day. The units are usually quite expensive. If the washer part or the dryer part fail, the whole unit is down. If you get the condenser dryer type, they take a long time to dry. I think I'd prefer to get either a stacked set or even a laundry center instead.

I think you have already been told, that yes, you could have a flood. Even if it didnt flood from that, the vibration underneath it could cause the pump and other things to leak, and that could cause a lot of damage. I asked above post, if you had someone below you, because, if you do, you could be paying out a whole lot of money. I dont understand why you would even want to risk, all the extra damage and problems, which will cost a bundle of money, when you can repair it for 100 or so, or better yet, replace the machine with another top loader for 350 or so. Either way, is a whole lot less than you will have to pay out if you get a flood or other water damage.