Adding a toilet will require 3"or larger drain line from base of toilet to city main and sloped the intire way. If the nearby toilet happens to be in center of house and add on toilet is to be on an outside wall,the nearby toilet has little effect unless house is on pier and beam or existing toilet drain runs near edge of foundation and new toilet. Replace toilet with washer in the above in most cases because few shower drains have capacity to carry a washer drain.
Hot and cold water supply can be extended to most anywhere desired but drains can be very difficult. Gas supply is by far easier to extend and can be located almost anywhere desired. On the average,adding a toilet tends to be more probmatic on slabs than any other remodel.

All of it will require your building's (and/or neighbor below's) permission to open the walls and tinker with stuff inside the wall. None of it is easy. Venting a dryer will be a big problem unless you choose a ventless dryer. Getting a gas line for it may be fairly straightforward. Getting the washer to drain may not be straightforward though, unless you drain it through an existing laundry sink. Creating a laundry standpipe in a condo can be done for sure. It just won't be cheap or easy. And you can't know how expensive and difficult until you have licensed plumber in to start assessing the piping. Adding a toilet on the other hand, will be the hardest to do, and will require the most disruption to your neighbor below to access the pipes.

If youre on a concrete slab you probably won't be able to do anything. Doubt you could get permission from the condo board to bring in jackhammers to break up the slab.

Thanks all! Here's some followups:

OK, I gather that the most problematic is the addition of toilet.
The current toilet is near an ouside wall on the other side of which is an outdoor balcony, which itself can easily be turned into an enclosed room.

After toilet, Is the next-most problematic - adding a dryer vent?

Or is the next-most difficult - draining a wash-machine?

Above all:
Is there any URL covering all the above scenario's geared to dummies? Basically I'd love diagrams on a one-page printable sheet.

P.S. I'm not sure if there's a concrete slab under bldg. It's a condo (apt.) one flight up inside a building. There are 2 levels of apts. beneath it, since it's graded, with the lowest level opening to ground at rear, and entry level opening to ground at front.

The sum of the answers you got basicly says"it would be by far more reasonable to either move or buy the adjoining condo and install passage doors." You obviously don't grasp the magnitude of what you have in mind. And no,there is no one page printout,more like a $5k engineers drawing and you can use those to have an arcatect make his drawings which you summit for permits, then,,,,,,,,,,,,,

Uh, perhaps I should also try posting a link to here on the Bath or Remodeling forum? It's constructive to get various feedbacks with the exception of those which border on assumptionalism.

P.S. just found this helpful URL:

Here is a link that might be useful: helpful url

Getting the opinion (and quotes) of several plumbers in person is the only opinion besides that of your condo association that will really be useful to you. Start with the condo association, as they control if you are allowed to open up the walls.

In the old time, typically a large family of ten people had only one toilet and you people are spoiled. Many houses today have three bedrooms and four toilets so they don't have to move that far to the nearest one. As for washing machine, I used to live in a rental flat and we had the machine draining tube hung over the kitchen sink and drained right in there, when the wash was done, we moved it to the corner.