I'm interested in installing a Bay Window. The Bay Window would be wider than the existing vinyl window. The window is on the first floor of a one floor addition that is wood framed, flat tar-like roof with slight pitch, and vinyl siding. The window would be about 4-5 feet wide and 2 -3 feet tall. The existing window is one of those small kitchen windows 1.5 feet wide and 2 - 2.5 feet tall.

Should I build additional supporting features into the exterior wall, such as a sill plate?

Are there standards for how much space should be around the window - between the window and ceiling, sink, cabinet, and backdoor?

Is an electrical plug underneath a window a hazard? There is currently a plug in the wall where the window will go. It is likely easier to move it down rather than to move it to the side.

Any information or suggestions would be much appreciated!

-Michael

I think my approach would be;
Purchase the window so I would know all of the rough in dimensions.
Remove the siding in the area or the window.
Measure the distance between the two studs beyond where the new window will fit.
Build a box out of 2 X4 to wide enough fit between the stud and high enough for the window to fit in plus 1/4".
Put internal studs in the box for the window width plus 1/4'.
Cut the house studs as necessary insuring that they are level.
Put your box in place and nail.
For appearance the top of windows are put at the same height as the top of doors when possible but there is no real rule on this. Before you put the box in place see what can be done about the electric. With the wall open you should be able to move an outlet, even if necessary to replace a length of wire. An outlet beneath a window is fine if that's where you want it. In choosing the height of the window keep in mind that you will have to build some kind roof over it since it projects out from the wall.

After putting your box in place go inside and cut out the drywall in the opening for the window. Install the window. The most important thing is to get your box level and square. After installing window begin building your roof over the window. This will most likely just be nailers attached to the studs at the proper height following the slope of the window then plywood sheathing attached. Install flashing and shingles. Reinstall siding, trim out window interior.

Good overall explanation